SMB Signing Disabled is a Medium risk vulnerability that is one of the most frequently found on networks around the world. This issue has been around since at long time but has proven either difficult to detect, difficult to resolve or prone to being overlooked entirely.

Contents: SMB Signing Disabled


What is SMB Signing Disabled?

Vulnerability Name:

SMB Signing Disabled

Test ID: 14300
Risk: Medium
Category: SMB/NetBIOS
Type: Attack
Summary: Signing is disabled on the remote SMB server. This can allow man-in-the-middle attacks against the SMB server. SMB servers should both require signatures as well as support them. 


Value Name: EnableSecuritySignature Data Type: REG_DWORD Data: 1 (enable) 
Value Name: RequireSecuritySignature Data Type: REG_DWORD Data: 1 (enable) 
On Windows Desktops: * HKEY_LOCAL_MACHINESystemCurrentControlSetServicesLanManWorkstationParameters 
Value Name: EnableSecuritySignature Data Type: REG_DWORD Data: 1 (enable)
Value Name: RequireSecuritySignature Data Type: REG_DWORD Data: 1 (enable)

Impact: Successful exploitation could allow remote attackers to gain sensitive information.

How do I Fix SMB Signing Disabled?

Enforce message signing in the host’s configuration. On Samba, the setting is called ‘server signing’. 
On Windows Servers: * HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesLanManServerParameters
Nist NVD (CVSS): N/A
CVSS Score: N/A
Microsoft Knowledge Base: 887429


Scanning For and Finding Vulnerabilities in SMB Signing Disabled

Use of Vulnerability Management tools, like Beyond Security’s beSECURE (Automated Vulnerability Detection Software), are standard practice for the discovery of this vulnerability. The primary failure of VA in finding this vulnerability is related to setting the proper scope and frequency of network scans. It is vital that the broadest range of hosts (active IPs) possible are scanned and that scanning is done frequently. We recommend weekly.

Your existing scanning solution or set of test tools should make this not just possible, but easy and affordable. If that is not the case, please consider beSECURE. 

Penetration Testing (pentest) for this Vulnerability

The SMB Signing Disabled vulnerability is prone to false positive reports by most vulnerability assessment solutions. beSECURE is alone in using behavior based testing that eliminates this issue. For all other VA tools security consultants will recommend confirmation by direct observation. In any case Penetration testing procedures for discovery of Vulnerabilities in SMB Signing Disabled produces the highest discovery accuracy rate, but the infrequency of this expensive form of testing degrades its value. The ideal would be to have pentesting accuracy and the frequency and scope possibilities of VA solutions, and this is accomplished only by beSECURE.

Security Updates on Vulnerabilities in SMB Signing Disabled

Given that this is one of the most frequently found vulnerabilities, there is ample information regarding mitigation online and very good reason to get it fixed. Hackers are also aware that this is a frequently found vulnerability and so its discovery and repair is that much more important. It is so well known and common that any network that has it present and unmitigated indicates “low hanging fruit” to attackers.

Confirming the Presence of Vulnerabilities in SMB Signing Disabled

beSECURE is currently testing for and finding this vulnerability with zero false positives. If your current set of tools is indicating that it is present but you think it is probably a false positive, please request a demonstration of beSECURE.

False positive/negatives

The secret killer of VA solution value is the false positive. There was an industry wide race to find the most vulnerabilities, including Vulnerabilities in SMB Signing Disabled ,and this resulted in benefit to poorly written tests that beef up scan reports by adding a high percentage of uncertainty. This may have sold a lot of systems some years ago, but it also stuck almost all VA solutions with deliberately inaccurate reporting that adds time to repairs that no administrator can afford. Beyond Security did not participate in this race to mutually assured destruction of the industry and to this day produces the most accurate and actionable reports available.

Patching/Repairing this Vulnerability

Run Windows Update and update the listed hotfixes or download and update mentioned hotfixes in the advisory

Vulnerabilities in SMB Signing Disabled is a Medium risk vulnerability that is also high frequency and high visibility. This is the most severe combination of security factors that exists and it is extremely important to find it on your network and fix it as soon as possible.

beSECURE can scan tens of thousands of IPs in large environments with segmented or distributed networks, and generate remediation tickets when vulnerabilities are found — and then track them within the system.