Linux Kernel up to 5.15.11 NFSD xdr_reserve_space buffer overflow

Summaryinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 5.15.11. Affected by this vulnerability is the function xdr_reserve_space of the component NFSD. The manipulation results in buffer overflow. This vulnerability is cataloged as CVE-2021-47107. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 5.15.11 (Operating System). Affected is the function xdr_reserve_space of the component NFSD. The manipulation with an unknown input leads to a buffer overflow vulnerability. CWE is classifying the issue as CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: NFSD: Fix READDIR buffer overflow If a client sends a READDIR count argument that is too small (say, zero), then the buffer size calculation in the new init_dirlist helper functions results in an underflow, allowing the XDR stream functions to write beyond the actual buffer. This calculation has always been suspect. NFSD has never sanity- checked the READDIR count argument, but the old entry encoders managed the problem correctly. With the commits below, entry encoding changed, exposing the underflow to the pointer arithmetic in xdr_reserve_space(). Modern NFS clients attempt to retrieve as much data as possible for each READDIR request. Also, we have no unit tests that exercise the behavior of READDIR at the lower bound of @count values. Thus this case was missed during testing.

The weakness was shared 03/04/2024. The advisory is shared for download at git.kernel.org. This vulnerability is traded as CVE-2021-47107. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 02/14/2025).

Upgrading to version 5.15.12 or 5.16 eliminates this vulnerability. Applying the patch eabc0aab98e5/53b1119a6e50 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 5.15.0
• 5.15.1
• 5.15.2
• 5.15.3
• 5.15.4
• 5.15.5
• 5.15.6
• 5.15.7
• 5.15.8
• 5.15.9
• 5.15.10
• 5.15.11

License

• open-source

Website

• Vendor: https://www.kernel.org/

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