CyberSecBulletin
CVE-2026-64284NVD status: Modified

Linux: Time-of-check Time-of-use (TOCTOU) Race Condition

Published Updated By the CyberSecBulletin desk

CVE-2026-64284 is a high-severity time-of-check time-of-use (TOCTOU) race condition vulnerability in Linux, with a CVSS 3.1 base score of 7.1 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 b3436d9b9b1affe1c3191ac9831308923f5f03c3, 4ad73ef0e7966ecfe67de0060537b4cb14d9acd4, f2ca2b5326211bd38490f0497eb583721ce0bbc0 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.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to b3436d9b9b1affe1c3191ac9831308923f5f03c3 or 4ad73ef0e7966ecfe67de0060537b4cb14d9acd4 or f2ca2b5326211bd38490f0497eb583721ce0bbc0 or 0ffedf43910e44b76c2c1db4e9fbf12b268190c1, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.12.96 or 6.18.39 or 7.1.4, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxf7f39c50edb9d336274371953275e0d3503b9b75 up to, but not including, b3436d9b9b1affe1c3191ac9831308923f5f03c3; f7f39c50edb9d336274371953275e0d3503b9b75 up to, but not including, 4ad73ef0e7966ecfe67de0060537b4cb14d9acd4; f7f39c50edb9d336274371953275e0d3503b9b75 up to, but not including, f2ca2b5326211bd38490f0497eb583721ce0bbc0; f7f39c50edb9d336274371953275e0d3503b9b75 up to, but not including, 0ffedf43910e44b76c2c1db4e9fbf12b268190c1; 6.12b3436d9b9b1affe1c3191ac9831308923f5f03c3, 4ad73ef0e7966ecfe67de0060537b4cb14d9acd4, f2ca2b5326211bd38490f0497eb583721ce0bbc0, 0ffedf43910e44b76c2c1db4e9fbf12b268190c1
LinuxLinux Kernel6.12 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, 7.1.46.12.96, 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
NoneNo data is disclosed.
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:N/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Ensure vendor's exit handler runs before fastpath userspace exits Move the handling of fastpath userspace exits into vendor code to ensure KVM runs vendor specific operations that need to run before userspace gains control of the vCPU. E.g. for VMX (and soon to be for SVM as well), KVM needs to flush the PML buffer prior to exiting to userspace, otherwise any memory written by the final KVM_RUN might never be flagged as dirty. Note, waiting to snapshot CR0 and CR3 until svm_handle_exit() is flawed in general, as that risks consuming stale state in a fastpath handler. That will be addressed in a future change.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Time-of-check Time-of-use (TOCTOU) Race Condition

The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.

How developers prevent this class of flaw

  • The most basic advice for TOCTOU vulnerabilities is to not perform a check before the use. This does not resolve the underlying issue of the execution of a function on a resource whose state and identity cannot be assured, but it does help to limit the false sense of security given by the check.
  • When the file being altered is owned by the current user and group, set the effective gid and uid to that of the current user and group when executing this statement.
  • Limit the interleaving of operations on files from multiple processes.

More Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities (CWE-367)

Timeline

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

References

Recent Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities

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