Linux Kernel up to 6.4.3 nfsd reply_cache_stats null pointer dereference

Summaryinfo

A vulnerability identified as critical has been detected in Linux Kernel up to 6.4.3. The impacted element is the function reply_cache_stats of the component nfsd. The manipulation leads to null pointer dereference. This vulnerability is referenced as CVE-2023-54276. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, has been found in Linux Kernel up to 6.4.3. This issue affects the function reply_cache_stats of the component nfsd. The manipulation with an unknown input leads to a null pointer dereference vulnerability. Using CWE to declare the problem leads to CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. Impacted is availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: nfsd: move init of percpu reply_cache_stats counters back to nfsd_init_net Commit f5f9d4a314da ("nfsd: move reply cache initialization into nfsd startup") moved the initialization of the reply cache into nfsd startup, but didn't account for the stats counters, which can be accessed before nfsd is ever started. The result can be a NULL pointer dereference when someone accesses /proc/fs/nfsd/reply_cache_stats while nfsd is still shut down. This is a regression and a user-triggerable oops in the right situation: - non-x86_64 arch - /proc/fs/nfsd is mounted in the namespace - nfsd is not started in the namespace - unprivileged user calls "cat /proc/fs/nfsd/reply_cache_stats" Although this is easy to trigger on some arches (like aarch64), on x86_64, calling this_cpu_ptr(NULL) evidently returns a pointer to the fixed_percpu_data. That struct looks just enough like a newly initialized percpu var to allow nfsd_reply_cache_stats_show to access it without Oopsing. Move the initialization of the per-net+per-cpu reply-cache counters back into nfsd_init_net, while leaving the rest of the reply cache allocations to be done at nfsd startup time. Kudos to Eirik who did most of the legwork to track this down.

The advisory is shared at git.kernel.org. The identification of this vulnerability is CVE-2023-54276 since 12/30/2025. The exploitation is known to be easy. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 281473 (Linux Distros Unpatched Vulnerability : CVE-2023-54276), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.4.4 eliminates this vulnerability. Applying the patch 3025d489f9c8984d1bf5916c4a20097ed80fca5c/8549384d0f65981761fe2077d04fa2a8d37b54e0/66a178177b2b3bb1d71e854c5e7bbb320eb0e566/768c408594b52d8531e1a8ab62e5620c19213e73/ed9ab7346e908496816cffdecd46932035f66e2e 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.

The vulnerability is also documented in the databases at Tenable (281473) and CERT Bund (WID-SEC-2025-2941). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Affected

• Debian Linux
• Amazon Linux 2
• IBM Power Hardware Management Console
• Red Hat Enterprise Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• Open Source Linux Kernel
• RESF Rocky Linux
• IBM DataPower Gateway

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.4.0
• 6.4.1
• 6.4.2
• 6.4.3

License

• open-source

Website

• Vendor: https://www.kernel.org/

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