Active DirectoryJune 1, 2023How to Find and Fix SMB Signing Disabled Vulnerability 

As a cybersecurity professional, I often encounter various vulnerabilities that hackers can exploit to gain unauthorized access to sensitive information. One such vulnerability is SMB signing disabled, commonly found in Microsoft Windows-based networks. SMB signing is crucial in protecting data integrity and preventing unauthorized access. In this blog, I will discuss what SMB signing disabled vulnerability is, its risks and consequences, common causes, how to detect it through penetration testing, and how to fix it. 

What is SMB Signing? 

Before we dive into the vulnerability, let’s familiarize ourselves with SMB signing. SMB signing is a security feature that adds a digital signature to each SMB packet transmitted between network devices. This signature ensures that the data exchanged between systems remains unchanged and has not been tampered with during transit.  

SMB signing offers several significant benefits for network security:

  1. It verifies the sender and recipient’s authenticity, ensuring communication between trusted parties.
  2. SMB signing prevents man-in-the-middle attacks by guaranteeing the integrity of the data exchanged.
  3. Enabling SMB signing enhances the overall security posture of an organization, safeguarding sensitive information and reducing the likelihood of data breaches. 

What is SMB Signing Disabled Vulnerability? 

SMB signing disabled vulnerability is a security vulnerability that allows an attacker to bypass SMB signing and modify the data in transit. This vulnerability can be exploited by attackers to gain unauthorized access to sensitive information or to carry out other malicious activities. When SMB signing is disabled, an attacker can intercept the communication and modify the data to carry out man-in-the-middle or relay attacks. 

Risks and Consequences of Disabling SMB Signing  

The risks and consequences of SMB signing disabled vulnerability are severe and can significantly impact an organization’s security posture. When SMB signing is disabled, an attacker can intercept the communication and modify the data without detection. This can lead to data theft, manipulation, and other malicious activities. 

Common Causes of SMB Signing Disabled Vulnerability 

There are several reasons why SMB Signing may be disabled on your network. One common cause is legacy systems that do not support SMB Signing. Another cause is misconfigured systems that have disabled SMB Signing for compatibility reasons. Some IT administrators may also disable SMB Signing to troubleshoot network issues without enabling it back. 

Detecting SMB Signing Disabled Vulnerability through Penetration Testing 

Penetration testing is essential to any cybersecurity program, as it helps organizations identify vulnerabilities and weaknesses in their security posture. To detect SMB signing disabled vulnerability, penetration testers can use various tools and techniques, such as network, port, and vulnerability scanners. 

How to Fix SMB Signing Disabled Vulnerability 

Fixing SMB Signing Disabled Vulnerability requires enabling SMB Signing on all systems in your network. To enable SMB Signing on Windows systems, follow these steps: 

  1. Open the Group Policy Editor by typing “gpedit.msc” in the Run dialog box. 
  2. Navigate to “Computer Configuration” > “Windows Settings” > “Security Settings” > “Local Policies” > “Security Options.” 
  3. Locate the “Microsoft network client: Digitally sign communications (always)” policy and set it to “Enabled.” 
  4. Locate the “Microsoft network client: Digitally sign communications (if server agrees)” policy and set it to “Enabled.” 

Once you have enabled SMB Signing on all systems, run a test to ensure that the vulnerability is fixed. 

Best Practices to Prevent SMB Signing Disabled Vulnerability 

To prevent SMB signing disabled vulnerability, organizations should follow some best practices, such as: 

  • Enabling SMB signing on all systems and devices 
  • Regularly updating systems with the latest security patches and software updates 
  • Using network segmentation to isolate critical systems and data 
  • Conducting regular penetration testing to identify vulnerabilities and weaknesses 

Other SMB Vulnerabilities to Watch Out For 

SMB Signing Disabled Vulnerability is not the only SMB vulnerability that can put your network at risk. Other SMB vulnerabilities to watch out for include: 

  1. EternalBlue: A vulnerability that allows attackers to execute remote code on a target system. 
  2. SMB Relay Attack: A vulnerability that allows attackers to replay SMB packets to gain unauthorized access. 
  3. SMB Null Session Attack: A vulnerability that allows attackers to connect to an SMB server without authentication. 

Importance of Regular Penetration Testing 

Regular penetration testing is essential to identify vulnerabilities and weaknesses in an organization’s security posture. It helps organizations to stay ahead of the attackers and prevent security breaches. Moreover, penetration testing helps organizations comply with regulatory requirements and industry standards, such as PCI DSS, HIPAA, and ISO 27001. 

Detect SMB Signing Disabled 

Administrators can verify the status of SMB signing checks using various tools. One such tool is the “Group Policy Management Console” (GPMC), where they can check the SMB signing configuration settings for domain controllers and clients.  

Nmap’s scripting engine (NSE) also allows users to use custom scripts that can perform SMB-related checks, like identifying SMB signing status. 


SMB Signing Disabled Vulnerability is a critical security vulnerability that can expose your network to cyber-attacks. To prevent this vulnerability, enable SMB Signing on all systems in your network and follow best practices to ensure the security of your network. Additionally, conduct regular security assessments and penetration tests to identify and fix vulnerabilities. By following these recommendations, you can protect your network from cyber threats and ensure the continuity of your business operations. 

Redfox Security is a diverse network of expert security consultants with a global mindset and a collaborative culture. If you are looking to improve your organization’s security posture, contact us today to discuss your security testing needs. Our team of security professionals can help you identify vulnerabilities and weaknesses in your systems, and provide recommendations to remediate them.

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Joe Zacharia

by Joe Zacharia

Senior Security Consultant | Redfox Security