Linux: Use After Free
CVE-2026-43091 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 b2faee12538b5b008eaef65a4201eb29cb5cefb3, b66920a3348c0f63ba18365248fa21fbf0b3a937, 438b1f668ad58f46ce699bb48e4698a7839e3f9e 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 0.13% 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 b2faee12538b5b008eaef65a4201eb29cb5cefb3 or b66920a3348c0f63ba18365248fa21fbf0b3a937 or 438b1f668ad58f46ce699bb48e4698a7839e3f9e or 3733fce2871c9bca9dd18a1a23b1432ea215a094, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.136 or 6.12.83 or 6.18.24 or 6.19.14, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | e1e551bc56302b80ff930c966f9985095fb1b70d up to, but not including, b2faee12538b5b008eaef65a4201eb29cb5cefb3; e1e551bc56302b80ff930c966f9985095fb1b70d up to, but not including, b66920a3348c0f63ba18365248fa21fbf0b3a937; e1e551bc56302b80ff930c966f9985095fb1b70d up to, but not including, 438b1f668ad58f46ce699bb48e4698a7839e3f9e; e1e551bc56302b80ff930c966f9985095fb1b70d up to, but not including, 3733fce2871c9bca9dd18a1a23b1432ea215a094; e1e551bc56302b80ff930c966f9985095fb1b70d up to, but not including, 33a3149dd81a1e2f52b80ee1e0fc380b39f3d028; e1e551bc56302b80ff930c966f9985095fb1b70d up to, but not including, 069daad4f2ae9c5c108131995529d5f02392c446; 4.9 | b2faee12538b5b008eaef65a4201eb29cb5cefb3, b66920a3348c0f63ba18365248fa21fbf0b3a937, 438b1f668ad58f46ce699bb48e4698a7839e3f9e, 3733fce2871c9bca9dd18a1a23b1432ea215a094, 33a3149dd81a1e2f52b80ee1e0fc380b39f3d028, 069daad4f2ae9c5c108131995529d5f02392c446 |
| Linux | Linux Kernel | 4.9 up to, but not including, 6.6.136; 6.7 up to, but not including, 6.12.83; 6.13 up to, but not including, 6.18.24; 6.19 up to, but not including, 6.19.14; 7.0 | 6.6.136, 6.12.83, 6.18.24, 6.19.14 |
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 CNA.
Official description
In the Linux kernel, the following vulnerability has been resolved: xfrm: Wait for RCU readers during policy netns exit xfrm_policy_fini() frees the policy_bydst hash tables after flushing the policy work items and deleting all policies, but it does not wait for concurrent RCU readers to leave their read-side critical sections first. The policy_bydst tables are published via rcu_assign_pointer() and are looked up through rcu_dereference_check(), so netns teardown must also wait for an RCU grace period before freeing the table memory. Fix this by adding synchronize_rcu() before freeing the policy hash tables.
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
- git.kernel.org/stable/c/069daad4f2ae9c5c108131995529d5f02392c446
- git.kernel.org/stable/c/33a3149dd81a1e2f52b80ee1e0fc380b39f3d028
- git.kernel.org/stable/c/3733fce2871c9bca9dd18a1a23b1432ea215a094
- git.kernel.org/stable/c/438b1f668ad58f46ce699bb48e4698a7839e3f9e
- git.kernel.org/stable/c/b66920a3348c0f63ba18365248fa21fbf0b3a937
Other references
Recent Use After Free vulnerabilities
- 8.8 High severity
- 8.8 High severity
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- 8.8 High severity
- 8.8 High severity
- 8.3 High severity
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