Linux: Use After Free
CVE-2025-21856 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 940d15254d2216b585558bcf36312da50074e711, 0505ff2936f166405d81d0d454a81d9c14124344, e26e8ac27351f457091459a0a355bacd06d5bb2b 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 0.22% 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 940d15254d2216b585558bcf36312da50074e711 or 0505ff2936f166405d81d0d454a81d9c14124344 or e26e8ac27351f457091459a0a355bacd06d5bb2b or 915e34d5ad35a6a9e56113f852ade4a730fb88f0, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.80 or 6.12.17 or 6.13.5, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 8c81ba20349daf9f7e58bb05a0c12f4b71813a30 up to, but not including, 940d15254d2216b585558bcf36312da50074e711; 8c81ba20349daf9f7e58bb05a0c12f4b71813a30 up to, but not including, 0505ff2936f166405d81d0d454a81d9c14124344; 8c81ba20349daf9f7e58bb05a0c12f4b71813a30 up to, but not including, e26e8ac27351f457091459a0a355bacd06d5bb2b; 8c81ba20349daf9f7e58bb05a0c12f4b71813a30 up to, but not including, 915e34d5ad35a6a9e56113f852ade4a730fb88f0; 6.3 | 940d15254d2216b585558bcf36312da50074e711, 0505ff2936f166405d81d0d454a81d9c14124344, e26e8ac27351f457091459a0a355bacd06d5bb2b, 915e34d5ad35a6a9e56113f852ade4a730fb88f0 |
| Linux | Linux Kernel | 6.3 up to, but not including, 6.6.80; 6.7 up to, but not including, 6.12.17; 6.13 up to, but not including, 6.13.5; 6.14 | 6.6.80, 6.12.17, 6.13.5 |
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 NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | NVD |
| CVSS 3.1 | 7.8 | High | CISA (ADP) |
Official description
In the Linux kernel, the following vulnerability has been resolved: s390/ism: add release function for struct device According to device_release() in /drivers/base/core.c, a device without a release function is a broken device and must be fixed. The current code directly frees the device after calling device_add() without waiting for other kernel parts to release their references. Thus, a reference could still be held to a struct device, e.g., by sysfs, leading to potential use-after-free issues if a proper release function is not set.
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
- 9.8 Critical 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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