CVE-2026-23455: In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_h323: check for z

Q: How do I fix CVE-2026-23455?

linux kernel: upgrade to 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.20, 6.19.10. Exact commands for each OS are on this page.

Q: Is CVE-2026-23455 being exploited?

CVE-2026-23455 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-23455 affect?

CVE-2026-23455 affects linux kernel. Severity is critical (CVSS 9.1). 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

Q: How urgent is CVE-2026-23455?

Priority 60/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.1REMOTEWATCHLISTUPGRADE

CVE-2026-23455 is a critical-severity flaw (CVSS 9.1) affecting linux kernel. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Critical severity
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.5% (top 25%)
CISA exploited list	No
Weakness	CWE-125
Published	2026-04-03
Last modified	2026-10-19

Publisher (CNA): kernel.org · Vendor: linux

Last updated 2026-10-19 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-03 16:16 UTCPublished CVE record published
2026-10-19 19:17 UTCUpdated Record last modified

linux linux kernel UPGRADE

Affected: >= 2.6.17 and < 5.10.253 · >= 5.11 and < 5.15.203 · >= 5.16 and < 6.1.167 · >= 6.2 and < 6.6.130 · >= 6.7 and < 6.12.78 · >= 6.13 and < 6.18.20 · >= 6.19 and < 6.19.10 · 7.0 rc1

Fixed in: 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.20, 6.19.10

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Exact fixes by distribution

Fedora 46 · python-googleapis-common-protos · FIXED · 1.75.5-1.fc46~bootstrap · FEDORA-2026-d911c4c4e6 · source

sudo dnf upgrade --advisory=FEDORA-2026-d911c4c4e6

Fedora ELN · see advisory · FIXED · FEDORA-2026-e3987c278f · source

sudo dnf upgrade --advisory=FEDORA-2026-e3987c278f

Debian 12 · linux · FIXED · 6.1.170-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.1.170-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · linux · FIXED · 6.12.85-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "6.12.85-1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 10 · kernel · FIXED · kernel-6.12.0-211.18.1.el10_2

sudo dnf upgrade --advisory=RHSA-2026:21557 rpm -q kernel

RHEL 10.0 Extended Update Support · kernel · FIXED · kernel-6.12.0-55.98.1.el10_0

sudo dnf upgrade --advisory=RHSA-2026:55445 rpm -q kernel

RHEL 7 Extended Lifecycle Support · kernel-rt · FIXED · kernel-rt-3.10.0-1160.155.1.rt56.1307.el7

sudo dnf upgrade --advisory=RHSA-2026:41236 rpm -q kernel-rt

RHEL 7 Extended Lifecycle Support · kernel · FIXED · kernel-3.10.0-1160.154.1.el7

sudo dnf upgrade --advisory=RHSA-2026:35844 rpm -q kernel

RHEL 8 · kernel-rt · FIXED · kernel-rt-4.18.0-553.126.1.rt7.467.el8_10

sudo dnf upgrade --advisory=RHSA-2026:21745 rpm -q kernel-rt

Amazon Linux 2023 · see advisory · FIXED · ALAS2023-2026-1681 · source

sudo dnf update --advisory=ALAS2023-2026-1681

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: cert-portal.siemens.com/productcert/html/ssa-019113.html
Write-up: cert-portal.siemens.com/productcert/html/ssa-082556.html
Write-up: cert-portal.siemens.com/productcert/html/ssa-457936.html

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-23455?

linux kernel: upgrade to 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.20, 6.19.10. Exact commands for each OS are on this page.

Is CVE-2026-23455 being exploited?

CVE-2026-23455 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-23455 affect?

CVE-2026-23455 affects linux kernel. Severity is critical (CVSS 9.1). 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

How urgent is CVE-2026-23455?

Priority 60/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Linux kernel vulnerabilities

Related CVEs

CVE-2026-63947 HIGH 8.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: Bluetooth: HIDP: fix missing length check
CVE-2026-98141 MEDIUM 5.5 UPGRADE In the Linux kernel, the following vulnerability has been resolved: ntfs: propagate reparse index insertion f
CVE-2026-64239 HIGH 7.8 UPGRADE In the Linux kernel, the following vulnerability has been resolved: mm/damon/sysfs-schemes: delete tried regi
CVE-2026-64236 MEDIUM 5.5 UPGRADE In the Linux kernel, the following vulnerability has been resolved: i2c: davinci: fix division by zero on mis
CVE-2026-98142 MEDIUM 5.5 UPGRADE In the Linux kernel, the following vulnerability has been resolved: drm/cirrus-qemu: Validate BAR0 size durin

References

← Back to latest CVEs