Linux: Use After Free
CVE-2025-21893 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 6afe2ea2daec156bd94ad2c5a6f4f4c48240dcd3, f6a3cf833188e897c97028cd7b926e3f2cb1a8c0, 75845c6c1a64483e9985302793dbf0dfa5f71e32 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.2% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 6afe2ea2daec156bd94ad2c5a6f4f4c48240dcd3 or f6a3cf833188e897c97028cd7b926e3f2cb1a8c0 or 75845c6c1a64483e9985302793dbf0dfa5f71e32, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.12.21 or 6.13.9, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 9578e327b2b4935a25d49e3891b8fcca9b6c10c6 up to, but not including, 6afe2ea2daec156bd94ad2c5a6f4f4c48240dcd3; 9578e327b2b4935a25d49e3891b8fcca9b6c10c6 up to, but not including, f6a3cf833188e897c97028cd7b926e3f2cb1a8c0; 9578e327b2b4935a25d49e3891b8fcca9b6c10c6 up to, but not including, 75845c6c1a64483e9985302793dbf0dfa5f71e32; 6.10 | 6afe2ea2daec156bd94ad2c5a6f4f4c48240dcd3, f6a3cf833188e897c97028cd7b926e3f2cb1a8c0, 75845c6c1a64483e9985302793dbf0dfa5f71e32 |
| Linux | Linux Kernel | 6.10 up to, but not including, 6.12.21; 6.13 up to, but not including, 6.13.9; 6.14 | 6.12.21, 6.13.9 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CISA (ADP).
Official description
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Recent Use After Free vulnerabilities
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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