Finding and Fixing Mountable NFS Shares, a High Risk Vulnerability

With Notes on Remediation, Penetration Testing, Disclosures, Patching and Exploits

Contents

  • Vital information on this issue
  • Scanning For and Finding Mountable NFS Shares
  • Penetration Testing (Pentest) for this Vulnerability
  • Security updates on Mountable NFS Shares
  • Disclosures related to Mountable NFS Shares
  • Confirming the Presence of Mountable NFS Shares
  • False positive/negatives
  • Patching/Repairing this vulnerability
  • Exploits related to Mountable NFS Shares

Vital Information on This Issue
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.


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://technet.microsoft.com/en-us/library/cc753731.aspx
Nist NVD (CVSS): AV:N/AC:L/Au:N/C:C/I:C/A:C
CVSS Score: 10.0
For more information on this also issue see: www.securiteam.com

Scanning For and Finding Mountable NFS Shares
Use of Vulnerability Management tools, like AVDS, 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 AVDS.

Penetration Testing (pentest) for this Vulnerability
The Mountable NFS Shares is prone to false positive reports by most vulnerability assessment solutions. AVDS 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 [name] 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 AVDS.

Security Updates on Mountable NFS Shares
For the most current updates on this vulnerability please check www.securiteam.com 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
http://www.vulnerabilityassessment.co.uk/nfs.htm https://nnc3.com/mags/Networking2/nfs/ch12_04.htm https://nmap.org/nsedoc/scripts/nfs-ls.html https://debian-handbook.info/browse/stable/sect.nfs-file-server.html

Confirming the Presence of Mountable NFS Shares Vulnerability
AVDS 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 contact us for a demonstration of AVDS.

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 Mountable NFS Shares ,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
https://technet.microsoft.com/en-us/library/cc753731.aspx
http://lpic2.unix.nl/ch10s02.html
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.

Exploits related to Mountable NFS Shares

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. For the needs of this article we will use the Metasploitable 2 which by default has the NFS service misconfigured.

https://pentestlab.wordpress.com/2013/01/20/nfs-misconfiguration/

Clients with old Sun/unix boxes routinely have NFS shares that nobody thinks about. Next time you're on an internal, keep this in mind:

http://josephpierini.blogspot.com/2012/03/exploiting-network-file-system-nfs.html

Please also visit www.securiteam.com to view any exploits available for this vulnerability, or search using "Mountable NFS Shares exploits".


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