CyberSecBulletin
CVE-2026-64091NVD status: Analyzed

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

Published Updated By the CyberSecBulletin desk

CVE-2026-64091 is a critical-severity time-of-check time-of-use (TOCTOU) race condition 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 e4236bf3ec8d6bb15d0d8d825dcf9933a7d6666b, 724a8eb4155669797c96b70d70e354284ae3b5a8, 211ea59988e1cba43cb0367ad65d379b56f9c3bd 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 0.43% chance of exploitation within 30 days, which is low compared with other CVEs.

Patch this week

Critical severity: a successful attack would have severe impact.

What to do

  1. Update Linux to e4236bf3ec8d6bb15d0d8d825dcf9933a7d6666b or 724a8eb4155669797c96b70d70e354284ae3b5a8 or 211ea59988e1cba43cb0367ad65d379b56f9c3bd or 65a1e67339aa8c95ac544b796946af388930ee23, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 3.17 or 4.5 or 4.10 or 4.15, whichever matches your release line, or a later version.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux16116dac23396e73c01eeee97b102e4833a4b205 up to, but not including, e4236bf3ec8d6bb15d0d8d825dcf9933a7d6666b; 16116dac23396e73c01eeee97b102e4833a4b205 up to, but not including, 724a8eb4155669797c96b70d70e354284ae3b5a8; 16116dac23396e73c01eeee97b102e4833a4b205 up to, but not including, 211ea59988e1cba43cb0367ad65d379b56f9c3bd; 16116dac23396e73c01eeee97b102e4833a4b205 up to, but not including, 65a1e67339aa8c95ac544b796946af388930ee23; 16116dac23396e73c01eeee97b102e4833a4b205 up to, but not including, b4d4efd4e351593c81e9293d4b4408d244fa5ee7; 16116dac23396e73c01eeee97b102e4833a4b205 up to, but not including, 4cc85aec8d3c9ab4dc716dc9f1ed36fca16b227f; 16116dac23396e73c01eeee97b102e4833a4b205 up to, but not including, 9a9c859457bc440a55773e01ff18b1bb5bab6836; 16116dac23396e73c01eeee97b102e4833a4b205 up to, but not including, 94d27005016be15ffc638b2ecbc4d58805ad7b48; and 9 more rangese4236bf3ec8d6bb15d0d8d825dcf9933a7d6666b, 724a8eb4155669797c96b70d70e354284ae3b5a8, 211ea59988e1cba43cb0367ad65d379b56f9c3bd, 65a1e67339aa8c95ac544b796946af388930ee23, b4d4efd4e351593c81e9293d4b4408d244fa5ee7, 4cc85aec8d3c9ab4dc716dc9f1ed36fca16b227f
LinuxLinux Kernel3.16.60 up to, but not including, 3.17; 4.4.217 up to, but not including, 4.5; 4.9.217 up to, but not including, 4.10; 4.14.174 up to, but not including, 4.15; 4.17.1 up to, but not including, 5.10.259; 5.11 up to, but not including, 5.15.210; 5.16 up to, but not including, 6.1.176; 6.2 up to, but not including, 6.6.143; and 5 more ranges3.17, 4.5, 4.10, 4.15, 5.10.259, 5.15.210

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: batman-adv: tt: fix TOCTOU race for reported vlans The local TT based TVLV is generated by first checking the number of VLANs which have at least one TT entry. A new buffer with the correct size for the VLANs is then allocated. Only then, the list of VLANs s used to fill the VLAN entries in the buffer. During this time, the meshif_vlan_list_lock is held. But the actual number of TT entries of each VLAN can still increase during this time - just not the number of VLANs in the list. But the prefilter used in the buffer size calculation might still cause an increase of the number of VLANs which need to be stored. Simply because a VLAN might now suddenly have at least one entry when it had none in the pre-alloc check - and then needs to occupy space which was not allocated. It is better to overestimate the buffer size at the beginning and then fill the buffer only with the VLANs which are not empty.

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. 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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