Linux: Improper Synchronization
CVE-2026-64556 is a high-severity improper synchronization 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 1d3e1102273f09180262496658e7eeed8a5a7b59, 4cdb1b3ab96eb1b7eb70bc5c82fede334bd60df2, 39358e856fb89e62e3c8d7389a2dc4ec33dbe90e 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 0.16% 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 1d3e1102273f09180262496658e7eeed8a5a7b59 or 4cdb1b3ab96eb1b7eb70bc5c82fede334bd60df2 or 39358e856fb89e62e3c8d7389a2dc4ec33dbe90e or a2d5d3ee7b6e3953114726b1521e62123ab5b043, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.1.191 or 6.6.145 or 6.12.96 or 6.18.39, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 2e498d0a74e5b88a6689ae1b811f247f91ff188e up to, but not including, 1d3e1102273f09180262496658e7eeed8a5a7b59; 2e498d0a74e5b88a6689ae1b811f247f91ff188e up to, but not including, 4cdb1b3ab96eb1b7eb70bc5c82fede334bd60df2; 2e498d0a74e5b88a6689ae1b811f247f91ff188e up to, but not including, 39358e856fb89e62e3c8d7389a2dc4ec33dbe90e; 2e498d0a74e5b88a6689ae1b811f247f91ff188e up to, but not including, a2d5d3ee7b6e3953114726b1521e62123ab5b043; 2e498d0a74e5b88a6689ae1b811f247f91ff188e up to, but not including, 06ccef0434e98058ddae7bcebc901f93d22b7653; 2e498d0a74e5b88a6689ae1b811f247f91ff188e up to, but not including, 037a3c43edfb597665dd34457cd22b14692f2ba3; 5.13 | 1d3e1102273f09180262496658e7eeed8a5a7b59, 4cdb1b3ab96eb1b7eb70bc5c82fede334bd60df2, 39358e856fb89e62e3c8d7389a2dc4ec33dbe90e, a2d5d3ee7b6e3953114726b1521e62123ab5b043, 06ccef0434e98058ddae7bcebc901f93d22b7653, 037a3c43edfb597665dd34457cd22b14692f2ba3 |
| Linux | Linux Kernel | 5.13 up to, but not including, 6.1.191; 6.2 up to, but not including, 6.6.145; 6.7 up to, but not including, 6.12.96; 6.13 up to, but not including, 6.18.39; 6.19 up to, but not including, 7.1.4; 7.2 | 6.1.191, 6.6.145, 6.12.96, 6.18.39, 7.1.4 |
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: Detach event groups during remove_on_exec perf_event_remove_on_exec() removes events by calling perf_event_exit_event(). For top-level events, this removes the event from the context with DETACH_EXIT only. This can leave inconsistent group state when a removed event is a group leader and the group contains siblings without remove_on_exec. If the group was active, the surviving siblings can remain active and attached to the removed leader's sibling list, but are no longer represented by a valid group leader on the PMU context active lists. A later close of the removed leader uses DETACH_GROUP and can promote the still-active siblings from this stale group state. The next schedule-in can then add an already-linked active_list entry again, corrupting the PMU context active list. With DEBUG_LIST enabled, this is caught as a list_add double-add in merge_sched_in(). Fix this by detaching group relationships when remove_on_exec removes an event. This preserves the existing task-exit and revoke behavior, while ensuring surviving siblings are ungrouped before the removed event leaves the context.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Synchronization
The product utilizes multiple threads, processes, components, or systems to allow temporary access to a shared resource that can only be exclusive to one process at a time, but it does not properly synchronize these actions, which might cause simultaneous accesses of this resource by multiple threads or processes.
How developers prevent this class of flaw
- Use industry standard APIs to synchronize your code.
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/037a3c43edfb597665dd34457cd22b14692f2ba3
- git.kernel.org/stable/c/06ccef0434e98058ddae7bcebc901f93d22b7653
- git.kernel.org/stable/c/1d3e1102273f09180262496658e7eeed8a5a7b59
- git.kernel.org/stable/c/39358e856fb89e62e3c8d7389a2dc4ec33dbe90e
- git.kernel.org/stable/c/4cdb1b3ab96eb1b7eb70bc5c82fede334bd60df2
- git.kernel.org/stable/c/a2d5d3ee7b6e3953114726b1521e62123ab5b043
Recent Improper Synchronization vulnerabilities
- 7.5 High severity
- 8.8 High severity
- 8.2 High severity
- 7.8 High severity
- 9.8 Critical severity
- 7.5 High severity
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