CyberSecBulletin
CVE-2026-23455NVD status: Modified

Linux: Out-of-bounds Read

Published Updated By the CyberSecBulletin desk

CVE-2026-23455 is a critical-severity out-of-bounds read vulnerability in Linux, with a CVSS 3.1 base score of 9.1 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 2121f5fbe88daff0f1fc5bc47d359426c74b86b0, 65fa92f79677858b14b9e4b7275f26639afe2710, 495e97af9e7249ee02b72bb1d0848a6efc3700f4 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 1.59% chance of exploitation within 30 days, higher than 76% of scored CVEs.

Patch this week

Critical severity: a successful attack would have severe impact.

What to do

  1. Update Linux to 2121f5fbe88daff0f1fc5bc47d359426c74b86b0 or 65fa92f79677858b14b9e4b7275f26639afe2710 or 495e97af9e7249ee02b72bb1d0848a6efc3700f4 or f5e4f4e4cdb75ec36802059a94195a31f193da60, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.10.253 or 5.15.203 or 6.1.167 or 6.6.130, 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
LinuxLinux5e35941d990123f155b02d5663e51a24f816b6f3 up to, but not including, 2121f5fbe88daff0f1fc5bc47d359426c74b86b0; 5e35941d990123f155b02d5663e51a24f816b6f3 up to, but not including, 65fa92f79677858b14b9e4b7275f26639afe2710; 5e35941d990123f155b02d5663e51a24f816b6f3 up to, but not including, 495e97af9e7249ee02b72bb1d0848a6efc3700f4; 5e35941d990123f155b02d5663e51a24f816b6f3 up to, but not including, f5e4f4e4cdb75ec36802059a94195a31f193da60; 5e35941d990123f155b02d5663e51a24f816b6f3 up to, but not including, 633e8f87dad32263f6a57dccdb873f042c062111; 5e35941d990123f155b02d5663e51a24f816b6f3 up to, but not including, 9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8; 5e35941d990123f155b02d5663e51a24f816b6f3 up to, but not including, b652b05d51003ac074b912684f9ec7486231717b; 5e35941d990123f155b02d5663e51a24f816b6f3 up to, but not including, f173d0f4c0f689173f8cdac79991043a4a89bf66; and 1 more ranges2121f5fbe88daff0f1fc5bc47d359426c74b86b0, 65fa92f79677858b14b9e4b7275f26639afe2710, 495e97af9e7249ee02b72bb1d0848a6efc3700f4, f5e4f4e4cdb75ec36802059a94195a31f193da60, 633e8f87dad32263f6a57dccdb873f042c062111, 9d00fe7d6d7c5b5f1065a6e042b54f2e44bd6df8
SiemensSIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)V3.1.6 and later; V3.1.5 and later; V3.1.7 and laterNot stated
SiemensSIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0)V3.1.6 and later; V3.1.5 and later; V3.1.7 and laterNot stated
SiemensSIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0)V3.1.6 and later; V3.1.5 and later; V3.1.7 and laterNot stated
SiemensSIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0)V3.1.6 and later; V3.1.5 and later; V3.1.7 and laterNot stated
SiemensSIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0)V3.1.6 and later; V3.1.5 and later; V3.1.7 and laterNot stated
LinuxLinux Kernel2.6.17 up to, but not including, 5.10.253; 5.11 up to, but not including, 5.15.203; 5.16 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, 6.18.20; 6.19 up to, but not including, 6.19.10; 7.05.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.20

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
NoneNothing can be modified.
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:N/A:H. Scored by CNA.

Official description

In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_h323: check for zero length in DecodeQ931() In DecodeQ931(), the UserUserIE code path reads a 16-bit length from the packet, then decrements it by 1 to skip the protocol discriminator byte before passing it to DecodeH323_UserInformation(). If the encoded length is 0, the decrement wraps to -1, which is then passed as a large value to the decoder, leading to an out-of-bounds read. Add a check to ensure len is positive after the decrement.

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

The underlying weakness: Out-of-bounds Read

The product reads data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that provides appropriate memory abstractions.

More Out-of-bounds Read vulnerabilities (CWE-125)

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 Out-of-bounds Read vulnerabilities

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