CVE-2026-89682

Received Received - Intake

Use-After-Free in Linux Kernel NFS Server

Publication date: 2026-09-11

Last updated on: 2026-09-13

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: fix fcache_disposal UAF by inlining dispose state into nfsd_net nfsd_file_dispose_list_delayed() defers fput() to nfsd service threads via a per-net freeme queue, preventing the shrinker and GC worker from bearing the cost of closing files (see ffb402596147). However, the queue lives in a separately-allocated struct nfsd_fcache_disposal that is freed by nfsd_free_fcache_disposal_net() during per-net teardown. The global shrinker, laundrette, and fsnotify callbacks can still be inside nfsd_file_dispose_list_delayed() dereferencing that pointer, causing a use-after-free. Inline the spinlock and freeme list directly into struct nfsd_net (as fcache_dispose_lock and fcache_dispose_list), eliminating the separately allocated struct nfsd_fcache_disposal entirely. These fields now have the same lifetime as the net namespace itself, so there is no dangling pointer to chase. nfsd_file_cache_start_net() now just initializes the inline fields and cannot fail due to allocation. nfsd_file_cache_shutdown_net() drains the inline list directly instead of freeing a separate struct. The alloc/free helpers are removed.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-09-11

Last Modified

2026-09-13

Generated

2026-10-02

AI Q&A

2026-09-12

EPSS Evaluated

2026-09-30

NVD

CVE-2026-89682

EUVD

EUVD-2026-76594

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability is a use-after-free (UAF) issue in the Linux kernel's NFS server (nfsd). It occurs when the kernel frees memory containing a queue used for deferred file cleanup while other parts of the kernel (shrinker, GC worker, callbacks) still try to access it. The fix involves moving the queue directly into the network namespace structure to ensure it is freed only when the namespace itself is destroyed.

Detection Guidance

This vulnerability is specific to the Linux kernel's NFS daemon (nfsd) and involves a use-after-free condition in the fcache_disposal mechanism. Detection requires checking kernel logs for related errors or kernel crashes. Commands like dmesg or journalctl -k may show traces of this issue. Ensure your kernel is updated to a patched version.

Impact Analysis

If exploited, this could lead to system crashes, data corruption, or privilege escalation. Attackers might trigger the UAF to cause instability or gain unauthorized access to sensitive data. Systems running vulnerable Linux kernels with NFS services enabled are at risk.

Compliance Impact

This vulnerability is a use-after-free issue in the Linux kernel's NFS server (nfsd) that could lead to memory corruption or crashes. It does not directly affect compliance with standards like GDPR or HIPAA, as those focus on data protection, privacy, and security controls rather than kernel memory management flaws.

Mitigation Strategies

Update the Linux kernel to a version that includes the fix for this vulnerability. The patch inlines the fcache_disposal state into nfsd_net, eliminating the use-after-free condition. Check your distribution's security advisories for the patched kernel version and apply it immediately.

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