Linux: Use After Free
CVE-2025-71159 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 c8385851a5435f4006281828d428e5d0b0bbf8af, 83f59076a1ae6f5c6845d6f7ed3a1a373d883684 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 0.25% 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 c8385851a5435f4006281828d428e5d0b0bbf8af or 83f59076a1ae6f5c6845d6f7ed3a1a373d883684, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.18.6 or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | e8513c012de75fd65e2df5499572bc6ef3f6e409 up to, but not including, c8385851a5435f4006281828d428e5d0b0bbf8af; e8513c012de75fd65e2df5499572bc6ef3f6e409 up to, but not including, 83f59076a1ae6f5c6845d6f7ed3a1a373d883684; 6.18 | c8385851a5435f4006281828d428e5d0b0bbf8af, 83f59076a1ae6f5c6845d6f7ed3a1a373d883684 |
| Linux | Linux Kernel | 6.18 up to, but not including, 6.18.6; 6.19 | 6.18.6 |
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 NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | CNA |
| CVSS 3.1 | 7.8 | High | NVD |
Official description
In the Linux kernel, the following vulnerability has been resolved: btrfs: fix use-after-free warning in btrfs_get_or_create_delayed_node() Previously, btrfs_get_or_create_delayed_node() set the delayed_node's refcount before acquiring the root->delayed_nodes lock. Commit e8513c012de7 ("btrfs: implement ref_tracker for delayed_nodes") moved refcount_set inside the critical section, which means there is no longer a memory barrier between setting the refcount and setting btrfs_inode->delayed_node. Without that barrier, the stores to node->refs and btrfs_inode->delayed_node may become visible out of order. Another thread can then read btrfs_inode->delayed_node and attempt to increment a refcount that hasn't been set yet, leading to a refcounting bug and a use-after-free warning. The fix is to move refcount_set back to where it was to take advantage of the implicit memory barrier provided by lock acquisition. Because the allocations now happen outside of the lock's critical section, they can use GFP_NOFS instead of GFP_ATOMIC.
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.
- 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
- 9.8 Critical severity
- 7.8 High severity
- 8.8 High severity
- 9.8 Critical severity
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