Linux: Use After Free
CVE-2025-39877 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 3858c44341ad49dc7544b19cc9f9ecffaa7cc50e, 60d7a3d2b985a395318faa1d88da6915fad11c19, 26d29b2ac87a2989071755f9828ebf839b560d4c 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 0.15% 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 3858c44341ad49dc7544b19cc9f9ecffaa7cc50e or 60d7a3d2b985a395318faa1d88da6915fad11c19 or 26d29b2ac87a2989071755f9828ebf839b560d4c or 4e87f461d61959647464a94d11ae15c011be58ce, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.1.153 or 6.6.107 or 6.12.48 or 6.16.8, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | a61ea561c87139992fe32afdee48a6f6b85d824a up to, but not including, 3858c44341ad49dc7544b19cc9f9ecffaa7cc50e; a61ea561c87139992fe32afdee48a6f6b85d824a up to, but not including, 60d7a3d2b985a395318faa1d88da6915fad11c19; a61ea561c87139992fe32afdee48a6f6b85d824a up to, but not including, 26d29b2ac87a2989071755f9828ebf839b560d4c; a61ea561c87139992fe32afdee48a6f6b85d824a up to, but not including, 4e87f461d61959647464a94d11ae15c011be58ce; a61ea561c87139992fe32afdee48a6f6b85d824a up to, but not including, 3260a3f0828e06f5f13fac69fb1999a6d60d9cff; 5.18 | 3858c44341ad49dc7544b19cc9f9ecffaa7cc50e, 60d7a3d2b985a395318faa1d88da6915fad11c19, 26d29b2ac87a2989071755f9828ebf839b560d4c, 4e87f461d61959647464a94d11ae15c011be58ce, 3260a3f0828e06f5f13fac69fb1999a6d60d9cff |
| Linux | Linux Kernel | 5.18 up to, but not including, 6.1.153; 6.2 up to, but not including, 6.6.107; 6.7 up to, but not including, 6.12.48; 6.13 up to, but not including, 6.16.8; 6.17 | 6.1.153, 6.6.107, 6.12.48, 6.16.8 |
| Debian | Debian Linux | 11.0 | Not stated |
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.
Official description
In the Linux kernel, the following vulnerability has been resolved: mm/damon/sysfs: fix use-after-free in state_show() state_show() reads kdamond->damon_ctx without holding damon_sysfs_lock. This allows a use-after-free race: CPU 0 CPU 1 ----- ----- state_show() damon_sysfs_turn_damon_on() ctx = kdamond->damon_ctx; mutex_lock(&damon_sysfs_lock); damon_destroy_ctx(kdamond->damon_ctx); kdamond->damon_ctx = NULL; mutex_unlock(&damon_sysfs_lock); damon_is_running(ctx); /* ctx is freed */ mutex_lock(&ctx->kdamond_lock); /* UAF */ (The race can also occur with damon_sysfs_kdamonds_rm_dirs() and damon_sysfs_kdamond_release(), which free or replace the context under damon_sysfs_lock.) Fix by taking damon_sysfs_lock before dereferencing the context, mirroring the locking used in pid_show(). The bug has existed since state_show() first accessed kdamond->damon_ctx.
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: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/26d29b2ac87a2989071755f9828ebf839b560d4c
- git.kernel.org/stable/c/3260a3f0828e06f5f13fac69fb1999a6d60d9cff
- git.kernel.org/stable/c/3858c44341ad49dc7544b19cc9f9ecffaa7cc50e
- git.kernel.org/stable/c/4e87f461d61959647464a94d11ae15c011be58ce
- git.kernel.org/stable/c/60d7a3d2b985a395318faa1d88da6915fad11c19
Third-party and government advisories
- lists.debian.org/debian-lts-announce/2025/10/msg00008.htmlMailing List, Third Party Advisory
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
Spotted an error? Tell us.