CVE-2025-21646: linux kernel — Fix

Description

In the Linux kernel, the following vulnerability has been resolved: afs: Fix the maximum cell name length The kafs filesystem limits the maximum length of a cell to 256 bytes, but a problem occurs if someone actually does that: kafs tries to create a directory under /proc/net/afs/ with the name of the cell, but that fails with a warning: WARNING: CPU: 0 PID: 9 at fs/proc/generic.c:405 because procfs limits the maximum filename length to 255. However, the DNS limits the maximum lookup length and, by extension, the maximum cell name, to 255 less two (length count and trailing NUL). Fix this by limiting the maximum acceptable cellname length to 253. This also allows us to be sure we can create the "/afs/.<cell>/" mountpoint too. Further, split the YFS VL record cell name maximum to be the 256 allowed by the protocol and ignore the record retrieved by YFSVL.GetCellName if it exceeds 253.

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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

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.8 — 5.10.234
linux	linux_kernel	5.11 — 5.15.177
linux	linux_kernel	5.16 — 6.1.125
linux	linux_kernel	6.2 — 6.6.72
linux	linux_kernel	6.7 — 6.12.10
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/7673030efe0f8ca1056d3849d61784c6caa052af https://git.kernel.org/stable/c/7922b1f058fe24a93730511dd0ae2e1630920096 https://git.kernel.org/stable/c/7cb3e77e9b4e6ffa325a5559393d3283c9af3d01 https://git.kernel.org/stable/c/8fd56ad6e7c90ac2bddb0741c6b248c8c5d56ac8 https://git.kernel.org/stable/c/9340385468d056bb700b8f28df236b81fc86a079 https://git.kernel.org/stable/c/aabe47cf5ac5e1db2ae0635f189d836f67024904

Other References

https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html

Frequently Asked Questions

What is CVE-2025-21646? +

In the Linux kernel, the following vulnerability has been resolved: afs: Fix the maximum cell name length The kafs filesystem limits the maximum length of a cell to 256 bytes, but a problem occurs if someone actually does that: kafs tries to create a directory under /proc/net/afs/ with the name of the cell, but that fails with a warning: WARNING: CPU: 0 PID: 9 at fs/proc/generic.c:405 because procfs limits the maximum filename length to 255. However, the DNS limits the maximum lookup length and, by extension, the maximum cell name, to 255 less two (length count and trailing NUL). Fix this by limiting the maximum acceptable cellname length to 253. This also allows us to be sure we can create the "/afs/.<cell>/" mountpoint too. Further, split the YFS VL record cell name maximum to be the 256 allowed by the protocol and ignore the record retrieved by YFSVL.GetCellName if it exceeds 253. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2025-21646? +

CVE-2025-21646 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-2025-21646? +

CVE-2025-21646 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-2025-21646? +

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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CVE-2025-21646