Linux: Concurrent Execution using Shared Resource with Improper Synchronization
CVE-2026-64136 is a critical-severity concurrent execution using shared resource with improper synchronization vulnerability in Linux, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 7585d4242f59185b084957fa077396e53dbf7c24, 7df1df6f40c0720d30206aa35c0343b962350e0d, 13fb413ae22a37c69341918a6d651d19a9b0b9b7 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 0.41% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Linux to 7585d4242f59185b084957fa077396e53dbf7c24 or 7df1df6f40c0720d30206aa35c0343b962350e0d or 13fb413ae22a37c69341918a6d651d19a9b0b9b7 or bf4ebdb19ff9b3cdf992b50715fe61633327416a, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.6.142 or 6.12.92 or 6.18.34 or 7.0.11, whichever matches your release line, or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 92d197ef7e9bb4994dae2bb17c2f19fa09d219a2 up to, but not including, 7585d4242f59185b084957fa077396e53dbf7c24; 953953abb66e52c224057ab91e404284fefeab62 up to, but not including, 7df1df6f40c0720d30206aa35c0343b962350e0d; 601dd3b79769b38d30b693c40afdb2a4b7edf9d0 up to, but not including, 13fb413ae22a37c69341918a6d651d19a9b0b9b7; 3969db6b22e3d90d8c5f22ac1a7fe0350a94c136 up to, but not including, bf4ebdb19ff9b3cdf992b50715fe61633327416a; 96c4af418586ee9a6aab61738644366426e05316 up to, but not including, e374f4e496fef8168784f93a4477d67be34485fd; 96c4af418586ee9a6aab61738644366426e05316 up to, but not including, 4d8690dace005a38e6dbde9ecce2da3ad85c7c41; 8c59eeeeffa1524ef57e173a89a1a3ff539888d5; 6.6.128 up to, but not including, 6.6.142; and 4 more ranges | 7585d4242f59185b084957fa077396e53dbf7c24, 7df1df6f40c0720d30206aa35c0343b962350e0d, 13fb413ae22a37c69341918a6d651d19a9b0b9b7, bf4ebdb19ff9b3cdf992b50715fe61633327416a, e374f4e496fef8168784f93a4477d67be34485fd, 4d8690dace005a38e6dbde9ecce2da3ad85c7c41 |
| Linux | Linux Kernel | 6.6.128 up to, but not including, 6.6.142; 6.12.75 up to, but not including, 6.12.92; 6.18.16 up to, but not including, 6.18.34; 6.19.6 up to, but not including, 7.0.11; 7.1 | 6.6.142, 6.12.92, 6.18.34, 7.0.11 |
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
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- 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:N/AC:L/PR:N/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: smb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked() Commit 96c4af418586 ("cifs: Fix locking usage for tcon fields") refactored cifs code to change cifs_tcp_ses_lock for tc_lock around tc_count changes. There was missing lock around tc_count increment inside smb2_find_smb_sess_tcon_unlocked().
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: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/13fb413ae22a37c69341918a6d651d19a9b0b9b7
- git.kernel.org/stable/c/4d8690dace005a38e6dbde9ecce2da3ad85c7c41
- git.kernel.org/stable/c/7df1df6f40c0720d30206aa35c0343b962350e0d
- git.kernel.org/stable/c/bf4ebdb19ff9b3cdf992b50715fe61633327416a
- git.kernel.org/stable/c/e374f4e496fef8168784f93a4477d67be34485fd
Other references
Recent Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities
- 9.8 Critical severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
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