CyberSecBulletin
CVE-2026-53250NVD status: Modified

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

Published Updated By the CyberSecBulletin desk

CVE-2026-53250 is a high-severity time-of-check time-of-use (TOCTOU) race condition vulnerability in Linux, with a CVSS 3.1 base score of 7.8 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 eb778aed8a9b2381668fcb1247ae4fa011224768, 0dfe05b938435892875e07771170051346412df9, bfdfd2706d5fb2cd496a1506e680daf979309c8b 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 0.1% 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 eb778aed8a9b2381668fcb1247ae4fa011224768 or 0dfe05b938435892875e07771170051346412df9 or bfdfd2706d5fb2cd496a1506e680daf979309c8b or 22ba97ea9cc1f63a0d0244fae38057ed452b6ac7, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.18.36 or 7.0.13, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux48eb03dd26304c24f03bdbb9382e89c8564e71df up to, but not including, eb778aed8a9b2381668fcb1247ae4fa011224768; 48eb03dd26304c24f03bdbb9382e89c8564e71df up to, but not including, 0dfe05b938435892875e07771170051346412df9; 48eb03dd26304c24f03bdbb9382e89c8564e71df up to, but not including, bfdfd2706d5fb2cd496a1506e680daf979309c8b; 48eb03dd26304c24f03bdbb9382e89c8564e71df up to, but not including, 22ba97ea9cc1f63a0d0244fae38057ed452b6ac7; 6.8eb778aed8a9b2381668fcb1247ae4fa011224768, 0dfe05b938435892875e07771170051346412df9, bfdfd2706d5fb2cd496a1506e680daf979309c8b, 22ba97ea9cc1f63a0d0244fae38057ed452b6ac7
LinuxLinux Kernel6.8 up to, but not including, 6.18.36; 6.19 up to, but not including, 7.0.13; 7.16.18.36, 7.0.13

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
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:U/C:H/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: xsk: cache csum_start/csum_offset to fix TOCTOU in xsk_skb_metadata() The TX metadata area resides in the UMEM buffer which is memory-mapped and concurrently writable by userspace. In xsk_skb_metadata(), csum_start and csum_offset are read from shared memory for bounds validation, then read again for skb assignment. A malicious userspace application can race to overwrite these values between the two reads, bypassing the bounds check and causing out-of-bounds memory access during checksum computation in the transmit path. Fix this by reading csum_start and csum_offset into local variables once, then using the local copies for both validation and assignment. Note that other metadata fields (flags, launch_time) and the cached csum fields may be mutually inconsistent due to concurrent userspace writes, but this is benign: the only security-critical invariant is that each field's validated value is the same one used, which local caching guarantees.

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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