CyberSecBulletin
CVE-2026-64034NVD status: Modified

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

Published Updated By the CyberSecBulletin desk

CVE-2026-64034 is a critical-severity time-of-check time-of-use (TOCTOU) race condition vulnerability in Linux, with a CVSS 3.1 base score of 9.3 out of 10. It can be exploited with local access to the system by an unauthenticated attacker, without any action from a user. The record lists versions a201c66edf2ebc6cfdc3813a889ba20fecebfae3, 70ad2dff8d052a85dfef15715b531f38a29108cf, 566f42fb67a7ebfed6650e407e5b72e6b3e83bf7 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 0.11% 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 a201c66edf2ebc6cfdc3813a889ba20fecebfae3 or 70ad2dff8d052a85dfef15715b531f38a29108cf or 566f42fb67a7ebfed6650e407e5b72e6b3e83bf7 or 6180a06bbc99fd9114b8db4be6c4d46e40f046ef, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.15.209 or 6.1.175 or 6.6.142 or 6.12.92, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxca9c54d2d6a5ab2430c4eda364c77125d62e5e0f up to, but not including, a201c66edf2ebc6cfdc3813a889ba20fecebfae3; ca9c54d2d6a5ab2430c4eda364c77125d62e5e0f up to, but not including, 70ad2dff8d052a85dfef15715b531f38a29108cf; ca9c54d2d6a5ab2430c4eda364c77125d62e5e0f up to, but not including, 566f42fb67a7ebfed6650e407e5b72e6b3e83bf7; ca9c54d2d6a5ab2430c4eda364c77125d62e5e0f up to, but not including, 6180a06bbc99fd9114b8db4be6c4d46e40f046ef; ca9c54d2d6a5ab2430c4eda364c77125d62e5e0f up to, but not including, 09ec063d87c2dd3fa6f3561361a017bd882e9f37; ca9c54d2d6a5ab2430c4eda364c77125d62e5e0f up to, but not including, 3c4db56ccd13dd020fbf43afabaee74a40ec75e4; ca9c54d2d6a5ab2430c4eda364c77125d62e5e0f up to, but not including, 35f0f0a2536a4d604b4dbad92c85c4a8fdebb870; 5.13a201c66edf2ebc6cfdc3813a889ba20fecebfae3, 70ad2dff8d052a85dfef15715b531f38a29108cf, 566f42fb67a7ebfed6650e407e5b72e6b3e83bf7, 6180a06bbc99fd9114b8db4be6c4d46e40f046ef, 09ec063d87c2dd3fa6f3561361a017bd882e9f37, 3c4db56ccd13dd020fbf43afabaee74a40ec75e4
LinuxLinux Kernel5.13 up to, but not including, 5.15.209; 5.16 up to, but not including, 6.1.175; 6.2 up to, but not including, 6.6.142; 6.7 up to, but not including, 6.12.92; 6.13 up to, but not including, 6.18.34; 6.19 up to, but not including, 7.0.11; 7.15.15.209, 6.1.175, 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
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
NoneNo account or login is needed.
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:N/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: net: mana: Fix TOCTOU double-fetch of hwc_msg_id from DMA buffer In mana_hwc_rx_event_handler(), resp->response.hwc_msg_id is read from DMA-coherent memory and bounds-checked, then mana_hwc_handle_resp() re-reads the same field from the same DMA buffer for test_bit() and pointer arithmetic. DMA-coherent memory is mapped uncacheable on x86 and is shared, unencrypted, in Confidential VMs (SEV-SNP/TDX), so each load goes directly to host-visible memory. A H/W can modify the value between the check and the use, bypassing the bounds validation. Fix this by reading hwc_msg_id exactly once using READ_ONCE() into a stack-local variable in mana_hwc_rx_event_handler(), and passing the validated value as a parameter to mana_hwc_handle_resp().

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: total).
  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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