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[Cyberpedia](https://www.paloaltonetworks.com/cyberpedia?ts=markdown) 2. [Threats](https://www.paloaltonetworks.com/cyberpedia/threat?ts=markdown) 3. [Cyber Attack](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack?ts=markdown) 4. [SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions?ts=markdown) Table of Contents * [What Is a Cyber Attack?](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack?ts=markdown) * [Threat Overview: Cyber Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#threat?ts=markdown) * [Cyber Attack Types at a Glance](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#cyber?ts=markdown) * [Global Cyber Attack Trends](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#global?ts=markdown) * [Cyber Attack Taxonomy](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#taxonomy?ts=markdown) * [Threat-Actor Landscape](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#landscape?ts=markdown) * [Attack Lifecycle and Methodologies](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#methodologies?ts=markdown) * [Technical Deep Dives](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#technical?ts=markdown) * [Cyber Attack Case Studies](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#studies?ts=markdown) * [Tools, Platforms, and Infrastructure](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#tools?ts=markdown) * [The Effect of Cyber Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#effect?ts=markdown) * [Detection, Response, and Intelligence](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#detection?ts=markdown) * [Emerging Cyber Attack Trends](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#trends?ts=markdown) * [Testing and Validation](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#testing?ts=markdown) * [Metrics and Continuous Improvement](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#metrics?ts=markdown) * [Cyber Attack FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack#faqs?ts=markdown) * What Are SMB Null Sessions? Risks, Detection \& Prevention * [SMB Null Sessions Explained](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#explained?ts=markdown) * [The Mechanics of Abuse: How Null Sessions Work](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#mechanics?ts=markdown) * [Valid Use Cases for SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#valid?ts=markdown) * [Risks of SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#risks?ts=markdown) * [Proactive Detection of SMB Null Session Abuse](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#proactive?ts=markdown) * [Remediation: How to Disable SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#remediation?ts=markdown) * [SMB Null Session FAQs](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#faqs?ts=markdown) * [What Is a DDoS Attack?](https://www.paloaltonetworks.com/cyberpedia/what-is-a-ddos-attack?ts=markdown) * [Threat Overview](https://www.paloaltonetworks.com/cyberpedia/what-is-a-ddos-attack#threat?ts=markdown) * [How Distributed Denial-of-Service Attacks Work](https://www.paloaltonetworks.com/cyberpedia/what-is-a-ddos-attack#how?ts=markdown) * [DDoS in Multistage Attack Campaigns](https://www.paloaltonetworks.com/cyberpedia/what-is-a-ddos-attack#ddos?ts=markdown) * [Real-World DDoS Incidents and Organizational Impact](https://www.paloaltonetworks.com/cyberpedia/what-is-a-ddos-attack#impact?ts=markdown) * [DDoS Attack Detection Indicators](https://www.paloaltonetworks.com/cyberpedia/what-is-a-ddos-attack#indicators?ts=markdown) * [DDoS Prevention and Mitigation](https://www.paloaltonetworks.com/cyberpedia/what-is-a-ddos-attack#mitigation?ts=markdown) * [DDoS Response and Recovery](https://www.paloaltonetworks.com/cyberpedia/what-is-a-ddos-attack#recovery?ts=markdown) * [Distributed Denial of Service FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-a-ddos-attack#faqs?ts=markdown) * [Process Injection Explained: Techniques, Evasion, and Defense](https://www.paloaltonetworks.com/cyberpedia/what-is-process-injection?ts=markdown) * [Process Injection Explained](https://www.paloaltonetworks.com/cyberpedia/what-is-process-injection#process?ts=markdown) * [Process Injection Step-by-Step.](https://www.paloaltonetworks.com/cyberpedia/what-is-process-injection#injection?ts=markdown) * [Advanced Process Injection and Evasion Techniques](https://www.paloaltonetworks.com/cyberpedia/what-is-process-injection#advanced?ts=markdown) * [Defending Against Process Injection](https://www.paloaltonetworks.com/cyberpedia/what-is-process-injection#defending?ts=markdown) * [FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-process-injection#faqs?ts=markdown) * [Dark Web Leak Sites: Key Insights for Security Decision Makers](https://www.paloaltonetworks.com/cyberpedia/what-is-a-dark-web-leak-site?ts=markdown) * [Dark Web Leak Sites Explained](https://www.paloaltonetworks.com/cyberpedia/what-is-a-dark-web-leak-site#dark?ts=markdown) * [Evolving Extortion Tactics](https://www.paloaltonetworks.com/cyberpedia/what-is-a-dark-web-leak-site#tactics?ts=markdown) * [The Role of Leak Sites in Ransomware Double Extortion](https://www.paloaltonetworks.com/cyberpedia/what-is-a-dark-web-leak-site#role?ts=markdown) * [Critical Risks Exposed by Data Leak Sites](https://www.paloaltonetworks.com/cyberpedia/what-is-a-dark-web-leak-site#critical?ts=markdown) * [Anatomy of a Dark Web Leak Site](https://www.paloaltonetworks.com/cyberpedia/what-is-a-dark-web-leak-site#anatomy?ts=markdown) * [Proactive Defense: How Organizations Can Mitigate Dark Web Leaks](https://www.paloaltonetworks.com/cyberpedia/what-is-a-dark-web-leak-site#proactive?ts=markdown) * [Dark Web Leak Site FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-a-dark-web-leak-site#faqs?ts=markdown) * [What Is a Zero-Day Attack? Risks, Examples, and Prevention](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention?ts=markdown) * [Zero-Day Attacks Explained](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention#explained?ts=markdown) * [Zero-Day Vulnerability vs. Zero-Day Attack vs. CVE](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention#vs?ts=markdown) * [How Zero-Day Exploits Work](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention#how?ts=markdown) * [Common Zero-Day Attack Vectors](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention#common?ts=markdown) * [Why Zero-Day Attacks Are So Effective and Their Consequences](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention#why?ts=markdown) * [How to Prevent and Mitigate Zero-Day Attacks](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention#prevent?ts=markdown) * [The Role of AI in Zero-Day Defense](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention#role?ts=markdown) * [Real-World Examples of Zero-Day Attacks](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention#examples?ts=markdown) * [Zero-Day Attacks FAQs](https://www.paloaltonetworks.com/cyberpedia/zero-day-attacks-explained-risks-examples-prevention#faqs?ts=markdown) * [What Is Lateral Movement?](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement?ts=markdown) * [Why Attackers Use Lateral Movement](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#why?ts=markdown) * [How Do Lateral Movement Attacks Work?](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#how?ts=markdown) * [Stages of a Lateral Movement Attack](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#stages?ts=markdown) * [Techniques Used in Lateral Movement](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#technicques?ts=markdown) * [Detection Strategies for Lateral Movement](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#detection?ts=markdown) * [Tools to Prevent Lateral Movement](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#tools?ts=markdown) * [Best Practices for Defense](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#best?ts=markdown) * [Recent Trends in Lateral Movement Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#recent?ts=markdown) * [Industry-Specific Challenges](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#industry?ts=markdown) * [Compliance and Regulatory Requirements](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#compliance?ts=markdown) * [Financial Impact and ROI Considerations](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#financial?ts=markdown) * [Common Mistakes to Avoid](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#common?ts=markdown) * [Lateral Movement FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement#faqs?ts=markdown) * [What is a Botnet?](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet?ts=markdown) * [How Botnets Work](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#how?ts=markdown) * [Why are Botnets Created?](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#why?ts=markdown) * [What are Botnets Used For?](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#what?ts=markdown) * [Types of Botnets](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#types?ts=markdown) * [Signs Your Device May Be in a Botnet](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#signs?ts=markdown) * [How to Protect Against Botnets](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#protect?ts=markdown) * [Why Botnets Lead to Long-Term Intrusions](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#intrusions?ts=markdown) * [How To Disable a Botnet](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#disable?ts=markdown) * [Tools and Techniques for Botnet Defense](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#tools?ts=markdown) * [Real-World Examples of Botnets](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#examples?ts=markdown) * [Botnet FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-botnet#faqs?ts=markdown) * [What is a Payload-Based Signature?](https://www.paloaltonetworks.com/cyberpedia/what-is-a-payload-based-signature?ts=markdown) * [Importance of Payload-Based Signatures](https://www.paloaltonetworks.com/cyberpedia/what-is-a-payload-based-signature#important?ts=markdown) * [How Payload-Based Signatures Work](https://www.paloaltonetworks.com/cyberpedia/what-is-a-payload-based-signature#how?ts=markdown) * [Advantages of Payload-Based Signatures](https://www.paloaltonetworks.com/cyberpedia/what-is-a-payload-based-signature#advantages?ts=markdown) * [Use Cases of Payload-Based Signatures in Cybersecurity](https://www.paloaltonetworks.com/cyberpedia/what-is-a-payload-based-signature#usecases?ts=markdown) * [Payload-Based Signatures FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-a-payload-based-signature#faqs?ts=markdown) * [What is Spyware?](https://www.paloaltonetworks.com/cyberpedia/what-is-spyware?ts=markdown) * [Cybercrime: The Underground Economy](https://www.paloaltonetworks.com/cyberpedia/cybercrime-the-underground-economy?ts=markdown) * [Products](https://www.paloaltonetworks.com/cyberpedia/cybercrime-the-underground-economy#products?ts=markdown) * [Services](https://www.paloaltonetworks.com/cyberpedia/cybercrime-the-underground-economy#services?ts=markdown) * [Cybercrime FAQs](https://www.paloaltonetworks.com/cyberpedia/cybercrime-the-underground-economy#faqs?ts=markdown) * [What Is Cross-Site Scripting (XSS)?](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting?ts=markdown) * [XSS Explained](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#xss?ts=markdown) * [Evolution in Attack Complexity](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#evolution?ts=markdown) * [Anatomy of a Cross-Site Scripting Attack](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#anatomy?ts=markdown) * [Integration in the Attack Lifecycle](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#integration?ts=markdown) * [Widespread Exposure in the Wild](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#widespread?ts=markdown) * [Cross-Site Scripting Detection and Indicators](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#indicators?ts=markdown) * [Prevention and Mitigation](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#mitigation?ts=markdown) * [Response and Recovery Post XSS Attack](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#response?ts=markdown) * [Strategic Cross-Site Scripting Risk Perspective](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#strategic?ts=markdown) * [Cross-Site Scripting FAQs](https://www.paloaltonetworks.com/cyberpedia/xss-cross-site-scripting#faqs?ts=markdown) * [What Is a Dictionary Attack?](https://www.paloaltonetworks.com/cyberpedia/dictionary-attack?ts=markdown) * [Dictionary Attack Explained](https://www.paloaltonetworks.com/cyberpedia/dictionary-attack#dictionary?ts=markdown) * [How Dictionary Attacks Work](https://www.paloaltonetworks.com/cyberpedia/dictionary-attack#how?ts=markdown) * [Dictionary Attack in the Attack Lifecycle](https://www.paloaltonetworks.com/cyberpedia/dictionary-attack#lifecycle?ts=markdown) * [Dictionary Attack in the Real World](https://www.paloaltonetworks.com/cyberpedia/dictionary-attack#examples?ts=markdown) * [Dictionary Attack Detection and Indicators](https://www.paloaltonetworks.com/cyberpedia/dictionary-attack#indicators?ts=markdown) * [Preventing and Mitigating Dictionary Attack](https://www.paloaltonetworks.com/cyberpedia/dictionary-attack#preventing?ts=markdown) * [Attack Response and Recovery](https://www.paloaltonetworks.com/cyberpedia/dictionary-attack#recovery?ts=markdown) * [Dictionary Attack FAQs](https://www.paloaltonetworks.com/cyberpedia/dictionary-attack#faqs?ts=markdown) * [What Is a Credential-Based Attack?](https://www.paloaltonetworks.com/cyberpedia/what-is-a-credential-based-attack?ts=markdown) * [Credential-Based Attack Overview](https://www.paloaltonetworks.com/cyberpedia/what-is-a-credential-based-attack#credential?ts=markdown) * [How Credential-Based Attacks Work](https://www.paloaltonetworks.com/cyberpedia/what-is-a-credential-based-attack#how?ts=markdown) * [Variations on Credential-Based Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-a-credential-based-attack#variations?ts=markdown) * [Preventing Credential-Based Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-a-credential-based-attack#preventing?ts=markdown) * [Credential-Based Attack FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-a-credential-based-attack#faqs?ts=markdown) * [What Is a Denial of Service (DoS) Attack?](https://www.paloaltonetworks.com/cyberpedia/what-is-a-denial-of-service-attack-dos?ts=markdown) * [How Denial-of-Service Attacks Work](https://www.paloaltonetworks.com/cyberpedia/what-is-a-denial-of-service-attack-dos#how?ts=markdown) * [Denial-of-Service in Adversary Campaigns](https://www.paloaltonetworks.com/cyberpedia/what-is-a-denial-of-service-attack-dos#denial?ts=markdown) * [Real-World Denial-of-Service Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-a-denial-of-service-attack-dos#attacks?ts=markdown) * [Detection and Indicators of Denial-of-Service Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-a-denial-of-service-attack-dos#detection?ts=markdown) * [Prevention and Mitigation of Denial-of-Service Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-a-denial-of-service-attack-dos#prevention?ts=markdown) * [Response and Recovery from Denial-of-Service Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-a-denial-of-service-attack-dos#response?ts=markdown) * [Operationalizing Denial-of-Service Defense](https://www.paloaltonetworks.com/cyberpedia/what-is-a-denial-of-service-attack-dos#defense?ts=markdown) * [DoS Attack FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-a-denial-of-service-attack-dos#faqs?ts=markdown) * [What Is Hacktivism?](https://www.paloaltonetworks.com/cyberpedia/hacktivism?ts=markdown) * [Hacktivism Explained](https://www.paloaltonetworks.com/cyberpedia/hacktivism#explained?ts=markdown) * [Origins and Definitions](https://www.paloaltonetworks.com/cyberpedia/hacktivism#origins?ts=markdown) * [Forms and Methods](https://www.paloaltonetworks.com/cyberpedia/hacktivism#forms?ts=markdown) * [Related Practices](https://www.paloaltonetworks.com/cyberpedia/hacktivism#related?ts=markdown) * [Who Do Hacktivists Target?](https://www.paloaltonetworks.com/cyberpedia/hacktivism#who?ts=markdown) * [What Motivates Hacktivists?](https://www.paloaltonetworks.com/cyberpedia/hacktivism#what?ts=markdown) * [Is Hacktivism Ethical?](https://www.paloaltonetworks.com/cyberpedia/hacktivism#ethical?ts=markdown) * [Hacktivism FAQs](https://www.paloaltonetworks.com/cyberpedia/hacktivism#faqs?ts=markdown) * [What Is CSRF (Cross-Site Request Forgery)?](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery?ts=markdown) * [CSRF Explained](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#csrf?ts=markdown) * [How Cross-Site Request Forgery Works](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#how?ts=markdown) * [Where CSRF Fits in the Broader Attack Lifecycle](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#where?ts=markdown) * [CSRF in Real-World Exploits](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#exploits?ts=markdown) * [Detecting CSRF Through Behavioral and Telemetry Signals](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#detecting?ts=markdown) * [Defending Against Cross-Site Request Forgery](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#defending?ts=markdown) * [Responding to a CSRF Incident](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#responding?ts=markdown) * [CSRF as a Strategic Business Risk](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#risk?ts=markdown) * [Key Priorities for CSRF Defense and Resilience](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#key?ts=markdown) * [Cross-Site Request Forgery FAQs](https://www.paloaltonetworks.com/cyberpedia/csrf-cross-site-request-forgery#faqs?ts=markdown) * [What Is Spear Phishing?](https://www.paloaltonetworks.com/cyberpedia/what-is-spear-phishing?ts=markdown) * [Spear Phishing Email Tactics](https://www.paloaltonetworks.com/cyberpedia/what-is-spear-phishing#what?ts=markdown) * [How Does Spear Phishing Work?](https://www.paloaltonetworks.com/cyberpedia/what-is-spear-phishing#how?ts=markdown) * [Types of Spear Phishing Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-spear-phishing#types?ts=markdown) * [Examples of Spear Phishing Attacks](https://www.paloaltonetworks.com/cyberpedia/what-is-spear-phishing#examples?ts=markdown) * [How to Protect Yourself from Spear Phishing](https://www.paloaltonetworks.com/cyberpedia/what-is-spear-phishing#protect?ts=markdown) * [If You Fall Victim to Spear Phishing](https://www.paloaltonetworks.com/cyberpedia/what-is-spear-phishing#victim?ts=markdown) * [Spear Phishing FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-spear-phishing#faq?ts=markdown) * [What Is Brute Force?](https://www.paloaltonetworks.com/cyberpedia/brute-force?ts=markdown) * [How Brute Force Functions as a Threat](https://www.paloaltonetworks.com/cyberpedia/brute-force#how?ts=markdown) * [How Brute Force Works in Practice](https://www.paloaltonetworks.com/cyberpedia/brute-force#practice?ts=markdown) * [Brute Force in Multistage Attack Campaigns](https://www.paloaltonetworks.com/cyberpedia/brute-force#brute?ts=markdown) * [Real-World Brute Force Campaigns and Outcomes](https://www.paloaltonetworks.com/cyberpedia/brute-force#outcomes?ts=markdown) * [Detection Patterns in Brute Force Attacks](https://www.paloaltonetworks.com/cyberpedia/brute-force#detection?ts=markdown) * [Practical Defense Against Brute Force Attacks](https://www.paloaltonetworks.com/cyberpedia/brute-force#defense?ts=markdown) * [Response and Recovery After a Brute Force Incident](https://www.paloaltonetworks.com/cyberpedia/brute-force#response?ts=markdown) * [Brute Force Attack FAQs](https://www.paloaltonetworks.com/cyberpedia/brute-force#faqs?ts=markdown) * [What is a Command and Control Attack?](https://www.paloaltonetworks.com/cyberpedia/command-and-control-explained?ts=markdown) * [How a Command and Control Attack Works](https://www.paloaltonetworks.com/cyberpedia/command-and-control-explained#how?ts=markdown) * [Types of Command and Control Techniques](https://www.paloaltonetworks.com/cyberpedia/command-and-control-explained#types?ts=markdown) * [Devices Targeted by C\&C](https://www.paloaltonetworks.com/cyberpedia/command-and-control-explained#devices?ts=markdown) * [What Hackers Can Accomplish Through Command and Control](https://www.paloaltonetworks.com/cyberpedia/command-and-control-explained#what?ts=markdown) * [Command and Control FAQs](https://www.paloaltonetworks.com/cyberpedia/command-and-control-explained#faqs?ts=markdown) * [What Is an Advanced Persistent Threat?](https://www.paloaltonetworks.com/cyberpedia/what-is-advanced-persistent-threat-apt?ts=markdown) * [Characteristics of Advanced Persistent Threats](https://www.paloaltonetworks.com/cyberpedia/what-is-advanced-persistent-threat-apt#characteristics?ts=markdown) * [What Techniques Are Used for APT Attacks?](https://www.paloaltonetworks.com/cyberpedia/what-is-advanced-persistent-threat-apt#techniques?ts=markdown) * [What Are the Stages of an APT Attack?](https://www.paloaltonetworks.com/cyberpedia/what-is-advanced-persistent-threat-apt#stages?ts=markdown) * [What Is the Defense Against APT?](https://www.paloaltonetworks.com/cyberpedia/what-is-advanced-persistent-threat-apt#defense?ts=markdown) * [Real-World Example of an APT Attack](https://www.paloaltonetworks.com/cyberpedia/what-is-advanced-persistent-threat-apt#realworld?ts=markdown) * [Advanced Persistent Threat FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-advanced-persistent-threat-apt#faqs?ts=markdown) * [What is an Exploit Kit?](https://www.paloaltonetworks.com/cyberpedia/what-is-an-exploit-kit?ts=markdown) * [Landing Page](https://www.paloaltonetworks.com/cyberpedia/what-is-an-exploit-kit#landing?ts=markdown) * [Exploit](https://www.paloaltonetworks.com/cyberpedia/what-is-an-exploit-kit#exploit?ts=markdown) * [Payload](https://www.paloaltonetworks.com/cyberpedia/what-is-an-exploit-kit#payload?ts=markdown) * [What Is Credential Stuffing?](https://www.paloaltonetworks.com/cyberpedia/credential-stuffing?ts=markdown) * [Credential Stuffing Explained](https://www.paloaltonetworks.com/cyberpedia/credential-stuffing#credential?ts=markdown) * [Automated Exploitation of Reused Credentials](https://www.paloaltonetworks.com/cyberpedia/credential-stuffing#automated?ts=markdown) * [Integration in the Attack Lifecycle](https://www.paloaltonetworks.com/cyberpedia/credential-stuffing#integration?ts=markdown) * [Credential Stuffing Attacks in the Real World](https://www.paloaltonetworks.com/cyberpedia/credential-stuffing#stuffing?ts=markdown) * [Responding and Recovering from Credential Stuffing](https://www.paloaltonetworks.com/cyberpedia/credential-stuffing#responding?ts=markdown) * [Credential Stuffing FAQs](https://www.paloaltonetworks.com/cyberpedia/credential-stuffing#faqs?ts=markdown) * [What Is Smishing?](https://www.paloaltonetworks.com/cyberpedia/what-is-smishing?ts=markdown) * [How to Spot a Smishing Attempt](https://www.paloaltonetworks.com/cyberpedia/what-is-smishing#spot-smishing-attempt?ts=markdown) * [How to Avoid Being Smished](https://www.paloaltonetworks.com/cyberpedia/what-is-smishing#avoid-being-smished?ts=markdown) * [Smishing FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-smishing#faqs?ts=markdown) * [What is Social Engineering?](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering?ts=markdown) * [The Role of Human Psychology in Social Engineering](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering#role?ts=markdown) * [How Has Social Engineering Evolved?](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering#historical?ts=markdown) * [How Does Social Engineering Work?](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering#how?ts=markdown) * [Phishing vs Social Engineering](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering#phishing?ts=markdown) * [What is BEC (Business Email Compromise)?](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering#bec?ts=markdown) * [Notable Social Engineering Incidents](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering#notable?ts=markdown) * [Social Engineering Prevention](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering#social?ts=markdown) * [Consequences of Social Engineering](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering#consequences?ts=markdown) * [Social Engineering FAQs](https://www.paloaltonetworks.com/cyberpedia/what-is-social-engineering#faqs?ts=markdown) * [What Is a Honeypot?](https://www.paloaltonetworks.com/cyberpedia/honeypots?ts=markdown) * [Threat Overview: Honeypot](https://www.paloaltonetworks.com/cyberpedia/honeypots#threat?ts=markdown) * [Honeypot Exploitation and Manipulation Techniques](https://www.paloaltonetworks.com/cyberpedia/honeypots#honeypot?ts=markdown) * [Positioning Honeypots in the Adversary Kill Chain](https://www.paloaltonetworks.com/cyberpedia/honeypots#positioning?ts=markdown) * [Honeypots in Practice: Breaches, Deception, and Blowback](https://www.paloaltonetworks.com/cyberpedia/honeypots#blowback?ts=markdown) * [Detecting Honeypot Manipulation and Adversary Tactics](https://www.paloaltonetworks.com/cyberpedia/honeypots#tactics?ts=markdown) * [Safeguards Against Honeypot Abuse and Exposure](https://www.paloaltonetworks.com/cyberpedia/honeypots#safeguards?ts=markdown) * [Responding to Honeypot Exploitation or Compromise](https://www.paloaltonetworks.com/cyberpedia/honeypots#compromise?ts=markdown) * [Honeypot FAQs](https://www.paloaltonetworks.com/cyberpedia/honeypots#faqs?ts=markdown) * [What Is Password Spraying?](https://www.paloaltonetworks.com/cyberpedia/password-spraying?ts=markdown) * [Password Spraying Explained](https://www.paloaltonetworks.com/cyberpedia/password-spraying#password?ts=markdown) * [How Password Spraying Works](https://www.paloaltonetworks.com/cyberpedia/password-spraying#works?ts=markdown) * [Password Spraying in the Broader Attack Lifecycle](https://www.paloaltonetworks.com/cyberpedia/password-spraying#attack?ts=markdown) * [Real-World Examples of Password Spraying Attacks](https://www.paloaltonetworks.com/cyberpedia/password-spraying#realworld?ts=markdown) * [Detection and Indicators](https://www.paloaltonetworks.com/cyberpedia/password-spraying#detection?ts=markdown) * [Preventing and Mitigating Password Spraying Attacks](https://www.paloaltonetworks.com/cyberpedia/password-spraying#mitigating?ts=markdown) * [Responding to Password Spraying](https://www.paloaltonetworks.com/cyberpedia/password-spraying#responding?ts=markdown) * [Password Spraying FAQs](https://www.paloaltonetworks.com/cyberpedia/password-spraying#faqs?ts=markdown) * [How to Break the Cyber Attack Lifecycle](https://www.paloaltonetworks.com/cyberpedia/how-to-break-the-cyber-attack-lifecycle?ts=markdown) * [1. Reconnaissance:](https://www.paloaltonetworks.com/cyberpedia/how-to-break-the-cyber-attack-lifecycle#reconnaissance?ts=markdown) * [2. Weaponization and Delivery:](https://www.paloaltonetworks.com/cyberpedia/how-to-break-the-cyber-attack-lifecycle#weaponization?ts=markdown) * [3. Exploitation:](https://www.paloaltonetworks.com/cyberpedia/how-to-break-the-cyber-attack-lifecycle#exploitation?ts=markdown) * [4. Installation:](https://www.paloaltonetworks.com/cyberpedia/how-to-break-the-cyber-attack-lifecycle#installation?ts=markdown) * [5. Command and Control:](https://www.paloaltonetworks.com/cyberpedia/how-to-break-the-cyber-attack-lifecycle#command?ts=markdown) * [6. Actions on the Objective:](https://www.paloaltonetworks.com/cyberpedia/how-to-break-the-cyber-attack-lifecycle#actions?ts=markdown) * [Cyber Attack Lifecycle FAQs](https://www.paloaltonetworks.com/cyberpedia/how-to-break-the-cyber-attack-lifecycle#faqs?ts=markdown) * [What Is Phishing?](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing?ts=markdown) * [Phishing Explained](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#phishing?ts=markdown) * [The Evolution of Phishing](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#?ts=markdown) * [The Anatomy of a Phishing Attack](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#anatomy?ts=markdown) * [Why Phishing Is Difficult to Detect](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#detect?ts=markdown) * [Types of Phishing](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#types?ts=markdown) * [Phishing Adversaries and Motives](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#motives?ts=markdown) * [The Psychology of Exploitation](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#psychology?ts=markdown) * [Lessons from Phishing Incidents](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#lessons?ts=markdown) * [Building a Modern Security Stack Against Phishing](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#building?ts=markdown) * [Building Organizational Immunity](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#immunity?ts=markdown) * [Phishing FAQ](https://www.paloaltonetworks.com/cyberpedia/what-is-phishing#faqs?ts=markdown) * [What Is a Rootkit?](https://www.paloaltonetworks.com/cyberpedia/rootkit?ts=markdown) * [Rootkit Classification and Technical Definition](https://www.paloaltonetworks.com/cyberpedia/rootkit#rootkit?ts=markdown) * [Types of Rootkits](https://www.paloaltonetworks.com/cyberpedia/rootkit#types?ts=markdown) * [Rootkit Installation and Execution Flow](https://www.paloaltonetworks.com/cyberpedia/rootkit#installation?ts=markdown) * [Integration in the Attack Lifecycle](https://www.paloaltonetworks.com/cyberpedia/rootkit#integration?ts=markdown) * [Cyberattacks Involving Rootkits in the News](https://www.paloaltonetworks.com/cyberpedia/rootkit#cyberattacks?ts=markdown) * [Rootkit Detection and Indicators](https://www.paloaltonetworks.com/cyberpedia/rootkit#indicators?ts=markdown) * [Prevention and Mitigation](https://www.paloaltonetworks.com/cyberpedia/rootkit#prevention?ts=markdown) * [Responding to Rootkit-Related Attacks](https://www.paloaltonetworks.com/cyberpedia/rootkit#responding?ts=markdown) * [Rootkit FAQs](https://www.paloaltonetworks.com/cyberpedia/rootkit#faqs?ts=markdown) * [Browser Cryptocurrency Mining](https://www.paloaltonetworks.com/cyberpedia/threat-brief-browser-cryptocurrency-mining?ts=markdown) * [How It Works](https://www.paloaltonetworks.com/cyberpedia/threat-brief-browser-cryptocurrency-mining#works?ts=markdown) * [How to Defend Against It](https://www.paloaltonetworks.com/cyberpedia/threat-brief-browser-cryptocurrency-mining#defend?ts=markdown) * [Browser Cryptocurrency Mining FAQs](https://www.paloaltonetworks.com/cyberpedia/threat-brief-browser-cryptocurrency-mining#faqs?ts=markdown) * [What Is Pretexting?](https://www.paloaltonetworks.com/cyberpedia/pretexting?ts=markdown) * [Pretexting Explained](https://www.paloaltonetworks.com/cyberpedia/pretexting#pretexting?ts=markdown) * [Evolution of the Attack Technique](https://www.paloaltonetworks.com/cyberpedia/pretexting#evolution?ts=markdown) * [How Pretexting Works](https://www.paloaltonetworks.com/cyberpedia/pretexting#how?ts=markdown) * [Integration in the Attack Lifecycle](https://www.paloaltonetworks.com/cyberpedia/pretexting#integration?ts=markdown) * [Real-World Examples](https://www.paloaltonetworks.com/cyberpedia/pretexting#examples?ts=markdown) * [Pretexting Detection Tactics in Live Environments](https://www.paloaltonetworks.com/cyberpedia/pretexting#detection?ts=markdown) * [Prevention and Mitigation](https://www.paloaltonetworks.com/cyberpedia/pretexting#mitigation?ts=markdown) * [Pretexting FAQs](https://www.paloaltonetworks.com/cyberpedia/pretexting#faqs?ts=markdown) * [What Is Cryptojacking?](https://www.paloaltonetworks.com/cyberpedia/cryptojacking?ts=markdown) * [Understanding Cryptojacking](https://www.paloaltonetworks.com/cyberpedia/cryptojacking#understanding?ts=markdown) * [Types of Cryptojacking and Resource Abuse Attacks](https://www.paloaltonetworks.com/cyberpedia/cryptojacking#types?ts=markdown) * [How Cryptojacking Works](https://www.paloaltonetworks.com/cyberpedia/cryptojacking#how?ts=markdown) * [Cryptojacking in the Adversary Kill Chain](https://www.paloaltonetworks.com/cyberpedia/cryptojacking#chain?ts=markdown) * [Real-World Cases of Cryptojacking](https://www.paloaltonetworks.com/cyberpedia/cryptojacking#cases?ts=markdown) * [Prevention and Mitigation](https://www.paloaltonetworks.com/cyberpedia/cryptojacking#prevention?ts=markdown) * [Response and Recovery](https://www.paloaltonetworks.com/cyberpedia/cryptojacking#response?ts=markdown) * [Cryptojacking FAQs](https://www.paloaltonetworks.com/cyberpedia/cryptojacking#faqs?ts=markdown) # What Are SMB Null Sessions? 5 min. read Table of Contents * * [SMB Null Sessions Explained](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#explained?ts=markdown) * [The Mechanics of Abuse: How Null Sessions Work](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#mechanics?ts=markdown) * [Valid Use Cases for SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#valid?ts=markdown) * [Risks of SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#risks?ts=markdown) * [Proactive Detection of SMB Null Session Abuse](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#proactive?ts=markdown) * [Remediation: How to Disable SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#remediation?ts=markdown) * [SMB Null Session FAQs](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#faqs?ts=markdown) 1. SMB Null Sessions Explained * * [SMB Null Sessions Explained](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#explained?ts=markdown) * [The Mechanics of Abuse: How Null Sessions Work](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#mechanics?ts=markdown) * [Valid Use Cases for SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#valid?ts=markdown) * [Risks of SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#risks?ts=markdown) * [Proactive Detection of SMB Null Session Abuse](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#proactive?ts=markdown) * [Remediation: How to Disable SMB Null Sessions](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#remediation?ts=markdown) * [SMB Null Session FAQs](https://www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions#faqs?ts=markdown) SMB null sessions are unauthenticated, anonymous connections to a Windows system using the Server Message Block protocol. Established without verifying the identity of the initiating user or application, they allow attackers to connect to the IPC$ share without valid credentials. This legacy vulnerability enables the unauthorized enumeration of users, groups, and password policies during network reconnaissance. Key Points * [**Broken Access Control**](https://owasp.org/www-project-top-ten/2017/A5_2017-Broken_Access_Control): SMB null sessions on domain-joined devices (e.g., workstations or servers) enable enumeration of Active Directory domain information via unauthenticated network connections. \* **Data Exposure**: Exploiting SMB null sessions may result in the collection of data that can be utilized to perform additional attacks against the internal network. \* **Impact**: Enables various Active Directory data to be enumerated, including domain accounts (i.e., user and computer accounts), domain groups, and the domain password policy without first obtaining valid domain credentials. \* **Detection**: Monitor for Event ID 4624 (Anonymous Logon) and Event ID 5140 (Access to Share) targeting IPC$. \* **Prevention**: Disable unauthenticated remote access to the named pipes and shares of domain-joined devices (e.g., workstations or servers). ## SMB Null Sessions Explained An SMB null session occurs when a connection is established to a Windows system over the Server Message Block protocol without the connecting party providing a valid username and password. While originally intended to allow legacy systems to perform network operations without first authenticating, this configuration has become a significant security liability in the modern threat landscape. Establishing a null session grants an anonymous user limited capabilities on the affected device. If the device is joined to an Active Directory (AD) domain, an attacker can enumerate various information configured for the target domain, including: * Retrieving lists of local and domain users * Identifying active network shares * Uncovering system security policies * Determining the specific operating system version and service pack level Such information is invaluable for attackers, as it provides a roadmap for subsequent privilege escalation or [lateral movement](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement?ts=markdown). While modern Windows Server versions no longer ask whether newly promoted AD forests should be compatible with legacy Windows NT-based systems and applications, older versions allowed System Administrators to select this option. If this compatibility option were selected during upgrades of existing AD environments, it would add the "Anonymous Users" group to the built-in "Pre-Windows 2000 Compatible Access" group. This is an often-overlooked important note because it results in "Anonymous Users" having read access to the Active Directory environment through membership to the "Pre-Windows 2000 Compatible Access" group. Modern security architectures, such as [zero trust](https://www.paloaltonetworks.com/cyberpedia/what-is-a-zero-trust-architecture?ts=markdown), advocate removing all unauthenticated pathways to ensure every request is explicitly verified. The Mechanics of Abuse: How Null Sessions Work ## The Mechanics of Abuse: How Null Sessions Work To comprehend the risk and secure SMB effectively, it is necessary to first understand the root cause of SMB null sessions. SMB null sessions leverage the Server Message Block (SMB) and Common Internet File System (CIFS) protocols. The specific target is the IPC$ share, a hidden administrative share essential for remote administration and inter-process communication. A standard null session connection command looks like this: ``` net use \\192.168.1.1\IPC$ "" /u:"" ``` When a Windows host is configured to allow this type of connection, the operating system issues a valid security token to an unauthenticated user. While this token has limited privileges, it often retains the "Everyone" permission set in older or misconfigured environments. Attackers leverage this access to interact with Named Pipes (e.g., "samr" (Security Account Manager), "lsarpc" (Local Security Authority), and "browser" (Computer Browser) that serve as interfaces for querying system information. ## Valid Use Cases for SMB Null Sessions Security professionals often ask why this vulnerability exists at all. While the default stance for any modern enterprise should be to disable null sessions entirely, there are edge cases where they are enabled for operational continuity. ### Legacy Application Support Older [operational technology (OT)](https://www.paloaltonetworks.com/cyberpedia/what-is-ot-security?ts=markdown) environments or legacy financial applications built for legacy Windows NT domains may rely on null sessions to poll servers for status updates without managing authentication tokens. Disabling null sessions in these fragile environments can lead to an immediate denial of service state for critical business processes. ### Specific Storage Appliance Configurations Certain network attached storage (NAS) appliances integrated into Windows domains may require null session access to perform name mapping or initial share enumeration before a user authenticates. In these scenarios, the device acts as a translation layer, and blocking anonymous enumeration can prevent legitimate users from browsing available file shares. ## Risks of SMB Null Sessions The presence of a null session vulnerability is rarely a direct path to escalated privileges within a domain, but it enables initial reconnaissance that lowers the cost of an attack. ### Enumeration via RID Brute Forcing The most significant risk posed by SMB null sessions is RID Brute Forcing. Every object in Active Directory has a Security Identifier (SID), which ends in a Relative Identifier (RID). The Administrator account always has a RID of 500, while the Guest account has a RID 501. Attackers use enumeration tools (e.g., enum4linux or rpcclient) to cycle through thousands of RID numbers via a null session. For each valid RID supplied, the server will respond with the corresponding username. This effectively provides an attacker with a verified list of valid usernames without first identifying valid domain credentials. This eliminates the guesswork in a brute-force attack; the attacker no longer needs to guess who to attack, only what their password is. ![RID brute forcing via an SMB null session](https://www.paloaltonetworks.com/content/dam/pan/en_US/images/cyberpedia/rid-brute-forcing-via-an-smb-null-session.webp "RID brute forcing via an SMB null session") RID brute forcing via an SMB null session ### Password Policy Reconnaissance Through the "lsarpc" pipe, attackers can query the domain's password policy. They can determine: * Minimum password length. * Password complexity requirements. * Account lockout thresholds (e.g., lockout after 5 failed attempts). ![Retrieving the domain password policy via an SMB null session](https://www.paloaltonetworks.com/content/dam/pan/en_US/images/cyberpedia/retrieving-the-domain-password-policy-via-an-smb-null-session.webp "Retrieving the domain password policy via an SMB null session") Retrieving the domain password policy via an SMB null session Armed with the username list (via RID cycling) and the lockout policy, an attacker can craft a password spray attack that stays just under the lockout threshold, significantly increasing their chances of success while evading detection. ## Proactive Detection of SMB Null Session Abuse Detecting null session abuse requires visibility into both network traffic and endpoint logs. [Security operation centers (SOCs)](https://www.paloaltonetworks.com/cyberpedia/what-is-a-soc?ts=markdown) should move beyond passive blocking to active detection of enumeration attempts. ### Identifying Abuse Signatures in Network Traffic Network security platforms, such as [Next-Generation Firewalls](https://www.paloaltonetworks.com/cyberpedia/what-is-a-next-generation-firewall-ngfw?ts=markdown), can detect the specific protocol handshake of a null session. You should monitor for SMB/CIFS traffic on port 445, where the "Session Setup AndX Request" contains an empty string for either the account name or the password. A sudden spike in IPC$ tree connect requests from a single internal IP address to multiple targets often indicates internal reconnaissance efforts. ### Windows Event Log Analysis On the Windows endpoint side, specific Event IDs are indicative of anonymous activity: * **Event ID 4624:** Look for "Logon Type: 3" (Network) combined with "ANONYMOUS LOGON" in the Subject fields. * **Event ID 5140 / 5145:** These events log access to a network share. A pivotal indicator is access to "\\IPC$" where the "SubjectUserName" is "ANONYMOUS LOGON". [Unit 42 research](https://unit42.paloaltonetworks.com/incident-response-report/) emphasizes that successful [ransomware attacks](https://www.paloaltonetworks.com/cyberpedia/ransomware-common-attack-methods?ts=markdown) often begin with this type of internal enumeration. Correlating these logs with subsequent authentication failures (Event ID 4625) provides high-fidelity alerts for active attacks. ## Remediation: How to Disable SMB Null Sessions Remediation should be handled via Group Policy to ensure consistency across the domain. ### Configuring the "RestrictAnonymous" Registry Key The core control for null sessions is the "RestrictAnonymous" registry value located at: "HKLM\\SYSTEM\\CurrentControlSet\\Control\\Lsa". | Value | Policy Name | Result | | 0 | None | Rely on default permissions; null sessions are permitted. | | 1 | Do not allow enumeration | Prevents listing of accounts and shares but allows some connectivity. | | 2 | No access without explicit anonymous permissions | Strictly prevents all anonymous access to the system (recommended). | |-------|--------------------------------------------------|-----------------------------------------------------------------------| *Table 1: Registry Modifications (RestrictAnonymous Settings)* ### Group Policy Objects (GPO) for Network Access Control For a scalable fix, configure the following Group Policy Object (GPO) settings under **Computer Configuration \> Windows Settings \> Security Settings \> Local Policies \> Security Options:** 1. **Network access:** Do not allow anonymous enumeration of SAM accounts: Set to Enabled. 2. **Network access:** Do not allow anonymous enumeration of SAM accounts and shares: Set to Enabled. 3. **Network access:** Let Everyone permissions apply to anonymous users: Set to Disabled. 4. **Network access:** Restrict clients allowed to make remote calls to SAM: Configure the security descriptor to only allow "Administrators". Implementing these changes effectively closes the reconnaissance loop, forcing attackers to operate blindly. ### The Critical Need for SMBv1 Deprecation Null sessions are most dangerous when combined with SMBv1, which lacks the security features of later versions. Organizations should disable SMBv1 entirely across the fleet and transition to SMBv3.1.1, which includes robust encryption and pre-authentication integrity checks. ### Comparison: Null Sessions vs. SMB Guest Access While both involve unauthenticated access, they serve different purposes. Null sessions connect to the IPC$ share specifically to facilitate RPC communication and enumeration. SMB Guest access, on the other hand, typically refers to accessing a specific file share where the "Guest" account has been granted permissions. Null sessions are an architectural bypass, whereas Guest access is a permissive file-sharing configuration. ## SMB Null Session FAQs ### Is an SMB null session the same as the Guest account? No. The Guest account is a specific disabled-by-default user account with a RID of 501. A null session is an unauthenticated connection state that uses no credentials, though it may sometimes inherit "Guest" or "Everyone" permissions depending on the system configuration. ### Will disabling null sessions break my printers? It is possible. Older Multi-Function Devices (MFDs) that scan to network folders using SMBv1 or legacy SMB implementations may fail if null sessions are strictly blocked (RestrictAnonymous = 2). It is recommended to test with **RestrictAnonymous = 1** first or upgrade the printer firmware. ### Can an attacker gain remote code execution (RCE) via a null session? Generally, no. A null session is primarily an information disclosure vulnerability. It allows an attacker to map the network. However, if the attacker discovers a weak password for a domain account with Local Administrator privileges on a domain-joined device, they can then fully authenticate to achieve RCE on the affected system. ### What tools do penetration testers use to exploit this? Security professionals use tools such as "enum4linux", "rpcclient", and the native Windows "net use" command to identify and exploit null session vulnerabilities during authorized assessments. ### Does this vulnerability affect Azure AD (Entra ID) joined devices? SMB null sessions are primarily an on-premises Active Directory and NTLM/Kerberos concern. Cloud-native environments using modern authentication protocols are generally not susceptible to traditional SMB null session enumeration, though misconfigured cloud VMs running Windows Server can still be vulnerable. Related Content [What Is Lateral Movement? Understand post-exploitation activities performed by attackers.](https://www.paloaltonetworks.com/cyberpedia/what-is-lateral-movement?ts=markdown) [What Is a Cyber Attack? Understand the evolution of modern cyber attacks.](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack?ts=markdown) [Unit 42 Incident Simulation and Testing Datasheet Determine the effectiveness of your security controls.](https://www.paloaltonetworks.com/resources/datasheets/unit-42-incident-simulation-and-testing-services?ts=markdown) [Penetration Testing Simulate real-world attack scenarios to test your detection and response capabilities.](https://www.paloaltonetworks.com/unit42/assess/penetration-testing?ts=markdown) ![Share page on facebook](https://www.paloaltonetworks.com/etc/clientlibs/clean/imgs/resources/facebook-circular-icon.svg) ![Share page on linkedin](https://www.paloaltonetworks.com/etc/clientlibs/clean/imgs/resources/linkedin-circular-icon.svg) [![Share page by an email](https://www.paloaltonetworks.com/etc/clientlibs/clean/imgs/resources/email-circular-icon.svg)](mailto:?subject=What%20Are%20SMB%20Null%20Sessions%3F%20Risks%2C%20Detection%20%26%20Prevention&body=Learn%20how%20SMB%20null%20sessions%20allow%20anonymous%20attackers%20to%20enumerate%20network%20data.%20Discover%20how%20to%20detect%20them%20and%20prevent%20lateral%20movement%20with%20an%20NGFW.%20at%20https%3A//www.paloaltonetworks.com/cyberpedia/what-are-smb-null-sessions) Back to Top [Previous](https://www.paloaltonetworks.com/cyberpedia/what-is-a-cyber-attack?ts=markdown) What Is a Cyber Attack? 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