CyberSecBulletin
CVE-2026-43383NVD status: Modified

Linux: Observable Timing Discrepancy

Published Updated By the CyberSecBulletin desk

CVE-2026-43383 is a critical-severity observable timing discrepancy vulnerability in Linux, with a CVSS 3.1 base score of 9.4 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 821c8751fdeecdeecabeb11704dd33439c9e4bbc, ff44ec94d4fc8348600a69de0a8fa1102c23bce8, 345a9530756528d7ca407663d659c3c40e75c3dd 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 0.54% 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 821c8751fdeecdeecabeb11704dd33439c9e4bbc or ff44ec94d4fc8348600a69de0a8fa1102c23bce8 or 345a9530756528d7ca407663d659c3c40e75c3dd or 5d305a95130a8d08b9545e47f1e18d29d59866cb, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.10.253 or 6.1.167 or 6.6.130 or 6.12.78, 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
LinuxLinuxcfb6eeb4c860592edd123fdea908d23c6ad1c7dc up to, but not including, 821c8751fdeecdeecabeb11704dd33439c9e4bbc; cfb6eeb4c860592edd123fdea908d23c6ad1c7dc up to, but not including, ff44ec94d4fc8348600a69de0a8fa1102c23bce8; cfb6eeb4c860592edd123fdea908d23c6ad1c7dc up to, but not including, 345a9530756528d7ca407663d659c3c40e75c3dd; cfb6eeb4c860592edd123fdea908d23c6ad1c7dc up to, but not including, 5d305a95130a8d08b9545e47f1e18d29d59866cb; cfb6eeb4c860592edd123fdea908d23c6ad1c7dc up to, but not including, 02669e2a4d207068edce7e8b5fafd85822018ce6; cfb6eeb4c860592edd123fdea908d23c6ad1c7dc up to, but not including, ae3831b44f477de048287493e184fc3ff913b624; cfb6eeb4c860592edd123fdea908d23c6ad1c7dc up to, but not including, b502e97e29d791ff7a8051f29a414535739be218; cfb6eeb4c860592edd123fdea908d23c6ad1c7dc up to, but not including, 46d0d6f50dab706637f4c18a470aac20a21900d3; and 1 more ranges821c8751fdeecdeecabeb11704dd33439c9e4bbc, ff44ec94d4fc8348600a69de0a8fa1102c23bce8, 345a9530756528d7ca407663d659c3c40e75c3dd, 5d305a95130a8d08b9545e47f1e18d29d59866cb, 02669e2a4d207068edce7e8b5fafd85822018ce6, ae3831b44f477de048287493e184fc3ff913b624
LinuxLinux Kernel2.6.20 up to, but not including, 5.10.253; 5.11 up to, but not including, 6.1.167; 6.2 up to, but not including, 6.6.130; 6.7 up to, but not including, 6.12.78; 6.13 up to, but not including, 6.18.19; 6.19 up to, but not including, 6.19.9; 7.05.10.253, 6.1.167, 6.6.130, 6.12.78, 6.18.19, 6.19.9

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
LowSome restricted data 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:L/I:H/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: net/tcp-md5: Fix MAC comparison to be constant-time To prevent timing attacks, MACs need to be compared in constant time. Use the appropriate helper function for this.

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

The underlying weakness: Observable Timing Discrepancy

Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.

More Observable Timing Discrepancy vulnerabilities (CWE-208)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Observable Timing Discrepancy vulnerabilities

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