CVE-2025-21846: linux kernel Null Dereference — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: acct: perform last write from workqueue In [1] it was reported that the acct(2) system call can be used to trigger NULL deref in cases where it is set to write to a file that triggers an internal lookup. This can e.g., happen when pointing acc(2) to /sys/power/resume. At the point the where the write to this file happens the calling task has already exited and called exit_fs(). A lookup will thus trigger a NULL-deref when accessing current->fs. Reorganize the code so that the the final write happens from the workqueue but with the caller's credentials. This preserves the (strange) permission model and has almost no regression risk. This api should stop to exist though.

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CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-476 CWE-476

Affected Products

Vendor	Product	Versions
linux	linux_kernel	2.6.12 — 6.1.130
linux	linux_kernel	6.2 — 6.6.80
linux	linux_kernel	6.7 — 6.12.17
linux	linux_kernel	6.13 — 6.13.5
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/56d5f3eba3f5de0efdd556de4ef381e109b973a9 https://git.kernel.org/stable/c/5a59ced8ffc71973d42c82484a719c8f6ac8f7f7 https://git.kernel.org/stable/c/5c928e14a2ccd99462f2351ead627b58075bb736 https://git.kernel.org/stable/c/5d5b936cfa4b0d5670ca7420ef165a074bc008eb https://git.kernel.org/stable/c/5ee8da9bea70dda492d61f075658939af33d8410 https://git.kernel.org/stable/c/8acbf4a88c6a98c8ed00afd1a7d1abcca9b4735e https://git.kernel.org/stable/c/a8136afca090412a36429cb6c2543c714d9c0f84 https://git.kernel.org/stable/c/b03782ae707cc45e65242c7cddd8e28f1c22cde5

Other References

https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html https://cert-portal.siemens.com/productcert/html/ssa-265688.html

Frequently Asked Questions

What is CVE-2025-21846? +

In the Linux kernel, the following vulnerability has been resolved: acct: perform last write from workqueue In [1] it was reported that the acct(2) system call can be used to trigger NULL deref in cases where it is set to write to a file that triggers an internal lookup. This can e.g., happen when pointing acc(2) to /sys/power/resume. At the point the where the write to this file happens the calling task has already exited and called exit_fs(). A lookup will thus trigger a NULL-deref when accessing current->fs. Reorganize the code so that the the final write happens from the workqueue but with the caller's credentials. This preserves the (strange) permission model and has almost no regression risk. This api should stop to exist though. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2025-21846? +

CVE-2025-21846 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2025-21846? +

CVE-2025-21846 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-21846? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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