Linux: Use After Free
CVE-2026-23248 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 c27dea9f50ed525facb62ef647dddc4722456e07, ac7ecb65af170a7fc193e7bd8be15dac84ec6a56, 77de62ad3de3967818c3dbe656b7336ebee461d2 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 0.14% 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 c27dea9f50ed525facb62ef647dddc4722456e07 or ac7ecb65af170a7fc193e7bd8be15dac84ec6a56 or 77de62ad3de3967818c3dbe656b7336ebee461d2, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.18.17 or 6.19.7, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | b709eb872e19a19607bbb6d2975bc264d59735cf up to, but not including, c27dea9f50ed525facb62ef647dddc4722456e07; b709eb872e19a19607bbb6d2975bc264d59735cf up to, but not including, ac7ecb65af170a7fc193e7bd8be15dac84ec6a56; b709eb872e19a19607bbb6d2975bc264d59735cf up to, but not including, 77de62ad3de3967818c3dbe656b7336ebee461d2; 6.14 | c27dea9f50ed525facb62ef647dddc4722456e07, ac7ecb65af170a7fc193e7bd8be15dac84ec6a56, 77de62ad3de3967818c3dbe656b7336ebee461d2 |
| Linux | Linux Kernel | 6.14 up to, but not including, 6.18.17; 6.19 up to, but not including, 6.19.7; 7.0 | 6.18.17, 6.19.7 |
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: perf/core: Fix refcount bug and potential UAF in perf_mmap Syzkaller reported a refcount_t: addition on 0; use-after-free warning in perf_mmap. The issue is caused by a race condition between a failing mmap() setup and a concurrent mmap() on a dependent event (e.g., using output redirection). In perf_mmap(), the ring_buffer (rb) is allocated and assigned to event->rb with the mmap_mutex held. The mutex is then released to perform map_range(). If map_range() fails, perf_mmap_close() is called to clean up. However, since the mutex was dropped, another thread attaching to this event (via inherited events or output redirection) can acquire the mutex, observe the valid event->rb pointer, and attempt to increment its reference count. If the cleanup path has already dropped the reference count to zero, this results in a use-after-free or refcount saturation warning. Fix this by extending the scope of mmap_mutex to cover the map_range() call. This ensures that the ring buffer initialization and mapping (or cleanup on failure) happens atomically effectively, preventing other threads from accessing a half-initialized or dying ring buffer.
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
- 8.8 High severity
- 7.5 High severity
- 8.8 High severity
- 7.5 High severity
Spotted an error? Tell us.