CyberSecBulletin
CVE-2026-64561NVD status: Analyzed

Linux: Concurrent Execution using Shared Resource with Improper Synchronization

Published Updated By the CyberSecBulletin desk

CVE-2026-64561 is a high-severity concurrent execution using shared resource with improper synchronization vulnerability in Linux, with a CVSS 3.1 base score of 8.8 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 62ef67af1878fa2cd066642f2f59e33ade95f637, 65c4f7a1028cf01a93a2762d679c289810ede990, 35e77467610c4a37cb0ff54ee56b85f73b1f5700 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 0.3% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 62ef67af1878fa2cd066642f2f59e33ade95f637 or 65c4f7a1028cf01a93a2762d679c289810ede990 or 35e77467610c4a37cb0ff54ee56b85f73b1f5700 or 0026dbb7de8ea76e97d6edf42fc3cc084564e2bf, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.15.218 or 6.1.183 or 6.6.148 or 6.12.101, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxf95eec9bed76d42194c23153cb1cc8f186bf91cb up to, but not including, 62ef67af1878fa2cd066642f2f59e33ade95f637; f95eec9bed76d42194c23153cb1cc8f186bf91cb up to, but not including, 65c4f7a1028cf01a93a2762d679c289810ede990; f95eec9bed76d42194c23153cb1cc8f186bf91cb up to, but not including, 35e77467610c4a37cb0ff54ee56b85f73b1f5700; f95eec9bed76d42194c23153cb1cc8f186bf91cb up to, but not including, 0026dbb7de8ea76e97d6edf42fc3cc084564e2bf; f95eec9bed76d42194c23153cb1cc8f186bf91cb up to, but not including, f3477a6a4164f15287444eda685b5f6405dbd1e5; f95eec9bed76d42194c23153cb1cc8f186bf91cb up to, but not including, bce0d3c26e2c761a4bf43c8949f333fc7374eb2d; f95eec9bed76d42194c23153cb1cc8f186bf91cb up to, but not including, 2abd5287f08319fa35764566b15c6e22cb1068db; 5.962ef67af1878fa2cd066642f2f59e33ade95f637, 65c4f7a1028cf01a93a2762d679c289810ede990, 35e77467610c4a37cb0ff54ee56b85f73b1f5700, 0026dbb7de8ea76e97d6edf42fc3cc084564e2bf, f3477a6a4164f15287444eda685b5f6405dbd1e5, bce0d3c26e2c761a4bf43c8949f333fc7374eb2d
LinuxLinux Kernel5.9 up to, but not including, 5.15.218; 5.16 up to, but not including, 6.1.183; 6.2 up to, but not including, 6.6.148; 6.7 up to, but not including, 6.12.101; 6.13 up to, but not including, 6.18.42; 6.19 up to, but not including, 7.1.6; 7.25.15.218, 6.1.183, 6.6.148, 6.12.101, 6.18.42, 7.1.6

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
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Check for invalid/obsolete root *after* making MMU pages available Check for a "stale" page fault, i.e. for an invalid and/or obsolete root, after making MMU pages available for the shadow MMU. If reclaiming shadow pages zaps an in-use root, i.e. marks it invalid, then KVM will attempt to map memory into an invalid root. On its own, populating an invalid root is "fine", but because child shadow pages inherit their parent's role, any children created during the map/fetch will be created as invalid pages, thus violating KVM's invariant that invalid pages are never on the list of active MMU pages. Note, the underlying flaw has existed since KVM first started tracking invalid roots in 2008 (commit 2e53d63acba7, "KVM: MMU: ignore zapped root pagetables"), but the true badness only came along in 2020 (Linux 5.9) with the invariant that invalid shadow pages can't be on the list of active pages. Note #2, inheriting role.invalid when creating child shadow pages is also far from ideal; that flaw will be addressed separately.

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).

More Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities (CWE-362)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Technical write-ups (may include proof of concept)

Recent Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities

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