Linux Kernel up to 6.12.20/6.13.8 Global Variable key_put use after free

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.12.20/6.13.8. It has been rated as critical. Affected by this vulnerability is the function key_put of the component Global Variable Handler. The manipulation leads to use after free. This vulnerability is referenced as CVE-2025-21893. No exploit is available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.12.20/6.13.8 and classified as critical. This issue affects the function key_put of the component Global Variable Handler. The manipulation with an unknown input leads to a use after free vulnerability. Using CWE to declare the problem leads to CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: keys: Fix UAF in key_put() Once a key's reference count has been reduced to 0, the garbage collector thread may destroy it at any time and so key_put() is not allowed to touch the key after that point. The most key_put() is normally allowed to do is to touch key_gc_work as that's a static global variable. However, in an effort to speed up the reclamation of quota, this is now done in key_put() once the key's usage is reduced to 0 - but now the code is looking at the key after the deadline, which is forbidden. Fix this by using a flag to indicate that a key can be gc'd now rather than looking at the key's refcount in the garbage collector.

The advisory is shared at git.kernel.org. The identification of this vulnerability is CVE-2025-21893 since 12/29/2024. The exploitation is known to be easy. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 04/15/2025).

The vulnerability scanner Nessus provides a plugin with the ID 234339 (Amazon Linux 2023 : bpftool, kernel6.12, kernel6.12-modules-extra (ALAS2023-2025-935)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.12.21 or 6.13.9 eliminates this vulnerability. Applying the patch 6afe2ea2daec156bd94ad2c5a6f4f4c48240dcd3/f6a3cf833188e897c97028cd7b926e3f2cb1a8c0/75845c6c1a64483e9985302793dbf0dfa5f71e32 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 vulnerability database at Tenable (234339). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.12.0
• 6.12.1
• 6.12.2
• 6.12.3
• 6.12.4
• 6.12.5
• 6.12.6
• 6.12.7
• 6.12.8
• 6.12.9
• 6.12.10
• 6.12.11
• 6.12.12
• 6.12.13
• 6.12.14
• 6.12.15
• 6.12.16
• 6.12.17
• 6.12.18
• 6.12.19
• 6.12.20
• 6.13.0
• 6.13.1
• 6.13.2
• 6.13.3
• 6.13.4
• 6.13.5
• 6.13.6
• 6.13.7
• 6.13.8

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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