Linux: Use After Free
CVE-2025-21879 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 07836bc18f4ae42da4e922244f4685561c18755e, 5e79d26014f9386387575b9ed60d342057cee49b, 59f37036bb7ab3d554c24abc856aabca01126414 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 0.21% 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 07836bc18f4ae42da4e922244f4685561c18755e or 5e79d26014f9386387575b9ed60d342057cee49b or 59f37036bb7ab3d554c24abc856aabca01126414, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.13.6 or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | fef55c4d9c9c22264d2b2ceae1e26922cb6129a5 up to, but not including, 07836bc18f4ae42da4e922244f4685561c18755e; 1020443840569535f6025a855958f07ea3eebf71 up to, but not including, 5e79d26014f9386387575b9ed60d342057cee49b; 1020443840569535f6025a855958f07ea3eebf71 up to, but not including, 59f37036bb7ab3d554c24abc856aabca01126414; 6.13 | 07836bc18f4ae42da4e922244f4685561c18755e, 5e79d26014f9386387575b9ed60d342057cee49b, 59f37036bb7ab3d554c24abc856aabca01126414 |
| Linux | Linux Kernel | 6.13 up to, but not including, 6.13.6; 6.14 | 6.13.6 |
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: btrfs: fix use-after-free on inode when scanning root during em shrinking At btrfs_scan_root() we are accessing the inode's root (and fs_info) in a call to btrfs_fs_closing() after we have scheduled the inode for a delayed iput, and that can result in a use-after-free on the inode in case the cleaner kthread does the iput before we dereference the inode in the call to btrfs_fs_closing(). Fix this by using the fs_info stored already in a local variable instead of doing inode->root->fs_info.
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
Other references
Recent Use After Free vulnerabilities
- 7.8 High severity
- 7.8 High severity
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- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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