Vulnerabilities in NULL Session Available (SMB) is a Low risk vulnerability that is one of the most frequently found on networks around the world. This issue has been around since at least 1990 but has proven either difficult to detect, difficult to resolve or prone to being overlooked entirely.


Vital Information on This Issue

Vulnerability Name:

NULL Session Available (SMB)

Test ID: 10637
Risk: Low
Category: Policy Checks
Type: Attack
Summary: The remote host is running one of the Microsoft Windows operating systems. It was possible to log into it using a NULL session. A NULL session (no login/password) allows to get information about the remote host.
Solution: Disabling Logging of Anonymous Logon Events (on Windows XP and later) You can completely disable anonymous logons (aka NULL sessions), but doing so might affect accessibility by users in trusting domains. Before changing policies throughout your domain, we suggest testing them on a limited number of systems. Windows XP and later provide the six policies listed below for controlling what information can be accessed anonymously. (These policies are in the Microsoft Management Console-MMC-Local Security Policy snap-in under Computer Configuration\Windows Settings\SecuritySettings\Local Policies\SecurityOptions.)

1. Network access: Allow anonymous SID/Name translation
2. Network access: Do not allow anonymous enumeration of SAM accounts
3. Network access: Do not allow anonymous enumeration of SAM accounts and shares
4. Network access: Let Everyone permissions apply to anonymous users
5. Network access: Named Pipes that can be accessed anonymously
6. Network access: Shares that can be accessed anonymously 

The default values for these policies are acceptable for servers on a typical internal LAN. For hardened servers, such as Internet servers, we recommend disabling policies 1 and 4, enabling policies 2 and 3, and specifying empty lists for policies 5 and 6. 
You can’t specifically disable logging of anonymous logon events. In general, trying to prevent Windows from logging “noise” is futile. The only approach that works is to implement a log management solution that filters out the noise for you.

CVE: CVE-1999-0519



CVSS Score: 7.5

Scanning For and Finding Vulnerabilities in NULL Session Available (SMB)

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. Learn more or request a trial.

Penetration Testing (pentest) for this Vulnerability

The Vulnerabilities in NULL Session Available (SMB) 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 NULL Session Available (SMB) 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 NULL Session Available (SMB)

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.

Disclosures related to this vulnerability

Confirming the Presence of Vulnerabilities in NULL Session Available (SMB)

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 NULL Session Available (SMB), 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

Vulnerabilities in NULL Session Available (SMB) is a Low 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.

Exploits related to Vulnerabilities in NULL Session Available (SMB)

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