Linux: Concurrent Execution using Shared Resource with Improper Synchronization
CVE-2026-63952 is a high-severity concurrent execution using shared resource with improper synchronization vulnerability in Linux, with a CVSS 3.1 base score of 8.4 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 b3f4f82d1315f1439059a83d1c22c51a5b43d99e, 3be2a24f7f72ad7321ed6ad1715b956a4527bcf4, 0995d1f79aed8ccbf62056189dd53fd19726ea08 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 b3f4f82d1315f1439059a83d1c22c51a5b43d99e or 3be2a24f7f72ad7321ed6ad1715b956a4527bcf4 or 0995d1f79aed8ccbf62056189dd53fd19726ea08 or 555702282d4536a865dfffb1cd4f6028f196e7e8, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.143 or 6.12.93 or 6.18.35 or 7.0.12, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | c4f75bc8bd6b3d62665e1f5400c419540edb5601 up to, but not including, b3f4f82d1315f1439059a83d1c22c51a5b43d99e; c4f75bc8bd6b3d62665e1f5400c419540edb5601 up to, but not including, 3be2a24f7f72ad7321ed6ad1715b956a4527bcf4; c4f75bc8bd6b3d62665e1f5400c419540edb5601 up to, but not including, 0995d1f79aed8ccbf62056189dd53fd19726ea08; c4f75bc8bd6b3d62665e1f5400c419540edb5601 up to, but not including, 555702282d4536a865dfffb1cd4f6028f196e7e8; c4f75bc8bd6b3d62665e1f5400c419540edb5601 up to, but not including, 3b041514cb6eae45869b020f743c14d983363222; 6.3 | b3f4f82d1315f1439059a83d1c22c51a5b43d99e, 3be2a24f7f72ad7321ed6ad1715b956a4527bcf4, 0995d1f79aed8ccbf62056189dd53fd19726ea08, 555702282d4536a865dfffb1cd4f6028f196e7e8, 3b041514cb6eae45869b020f743c14d983363222 |
| Linux | Linux Kernel | 6.3 up to, but not including, 6.6.143; 6.7 up to, but not including, 6.12.93; 6.13 up to, but not including, 6.18.35; 6.19 up to, but not including, 7.0.12; 7.1 | 6.6.143, 6.12.93, 6.18.35, 7.0.12 |
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
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N. Scored by CNA.
Official description
In the Linux kernel, the following vulnerability has been resolved: memfd: deny writeable mappings when implying SEAL_WRITE When SEAL_EXEC is added, SEAL_WRITE is implied to make W^X. But the implied seal is set after the check that makes sure the memfd can not have any writable mappings. This means one can use SEAL_EXEC to apply SEAL_WRITE while having writeable mappings. This breaks the contract that SEAL_WRITE provides and can be used by an attacker to pass a memfd that appears to be write sealed but can still be modified arbitrarily. Fix this by adding the implied seals before the call for mapping_deny_writable() is done.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Concurrent Execution using Shared Resource with Improper Synchronization
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
How developers prevent this class of flaw
- In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
- Use thread-safe capabilities such as the data access abstraction in Spring.
- Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring. Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).
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/0995d1f79aed8ccbf62056189dd53fd19726ea08
- git.kernel.org/stable/c/3b041514cb6eae45869b020f743c14d983363222
- git.kernel.org/stable/c/3be2a24f7f72ad7321ed6ad1715b956a4527bcf4
- git.kernel.org/stable/c/555702282d4536a865dfffb1cd4f6028f196e7e8
- git.kernel.org/stable/c/b3f4f82d1315f1439059a83d1c22c51a5b43d99e
Recent Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities
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- 9.8 Critical severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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