Mountable NFS Shares is a high-risk vulnerability that is one of the most frequently found on networks around the world. This issue has been around since at least but has proven either difficult to detect, difficult to resolve or prone to being overlooked entirely. As NFS Exported Share Information Disclosures outline, successful exploitation will allow remote attackers to mount an NFS file system in Ultrix or OSF, even if it is denied on the access list.
What is NFS Shares Vulnerability?
| Vulnerability Name: | Mountable NFS Shares (MS15-034) |
| Test ID: | 2306 |
| Risk: | High |
| Category: | NFS Services |
| Type: | Attack |
| Summary: | This test attempts to mount each exported NFS shares. Some old versions of nfsd do not do the proper security checking when it comes to NFS access controls, or the remote host may be badly configured. |
| Impact: | Successful exploitation will allow Remote attackers to mount an NFS file system in Ultrix or OSF, even if it is denied on the access list. |
| Solution: | Place the appropriate restrictions on all NFS shares or block NFS from outside access |
| CVE: | CVE-1999-0170 CVE-1999-0211 CVE-1999-0554 |
| More Information: | https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/cc753731(v=ws.11) |
| Nist NVD (CVSS): | AV:N/AC:L/Au:N/C:C/I:C/A:C |
| CVSS Score: | 10.0 |
How Do I Protect NFS Shares?
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 vulnerability assessment solutions 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.
Best-in-class vulnerability assessment solutions like beSECURE should make this not just possible, but easy and affordable. Learn more or request a trial.
How to Pen Test (pentest) for Mounted NFS Shares
The Mountable NFS Shares 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 vulnerability assessment tools, security consultants will recommend confirmation by direct observation. In any case, penetration testing tools for discovery of Mountable NFS Shares produces the highest discovery accuracy rate.
For the needs of this article we will use the Metasploitable 2 which by default has the NFS service misconfigured. http://josephpierini.blogspot.com/2012/03/exploiting-network-file-system-nfs.html.
However, the infrequency of this expensive form of testing degrades its value. The ideal would be to have pen testing accuracy and the frequency and scope possibilities of vulnerability assessment solutions, and this is accomplished by beSECURE.
What is NFS and What Makes the Mountable NFS Shares Vulnerability so Risky?
NFS stands for Network File System and it is a service that can be found in Unix systems. The purpose of NFS is to allow users to access shared directories in a network. However special effort needs to be done from system administrators in order to configure properly an NFS share. Organizations often have old Sun/unix boxes that use NFS shares that are routinely forgotten.
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 Mountable NFS Shares Vulnerability
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.
How to Patch/Repair this Mountable NFS Shares Vulnerability
https://technet.microsoft.com/en-us/library/cc753731.aspx
Place the appropriate restrictions on all NFS shares or block NFS from outside access.
Mountable NFS Shares is a high-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.