CVE-2026-42009: A flaw was found in gnutls

This month

HIGH 7.5REMOTEWATCHLISTMITIGATEMITIGATEDOWNGRADE

CVE-2026-42009 is a high-severity flaw (CVSS 7.5) affecting gnutls, hardened images, openshift container platform. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A flaw was found in gnutls. A remote attacker could exploit an issue in the Datagram Transport Layer Security (DTLS) packet reordering logic. The comparator function, responsible for ordering DTLS packets by sequence numbers, did not correctly handle packets with duplicate sequence numbers. This could lead to unstable packet ordering or undefined behavior, resulting in a denial of service.

Why this priority

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

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.3% (top 29%)
CISA exploited list	No
Weakness	CWE-475
Published	2026-05-18
Last modified	2026-10-26

Publisher (CNA): Red Hat, Inc. · Vendor: gnu · redhat

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-18 13:16 UTCPublished CVE record published
2026-10-26 18:17 UTCUpdated Record last modified

gnu gnutls MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy gnutls || rpm -q gnutls || gnutls --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

redhat hardened images MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy hardened-images || rpm -q hardened-images || hardened-images --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

redhat openshift container platform DOWNGRADE

Affected: 4.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.0

1. Check installed version

apt-cache policy openshift-container-platform || rpm -q openshift-container-platform || openshift-container-platform --version

2. No fixed release: DOWNGRADE to a release before 4.0 (Debian / Ubuntu)

apt-cache madison openshift-container-platform sudo apt install openshift-container-platform=<VERSION_BEFORE_4.0> sudo apt-mark hold openshift-container-platform

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list openshift-container-platform sudo dnf downgrade openshift-container-platform-<VERSION_BEFORE_4.0> sudo dnf versionlock add openshift-container-platform

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

redhat enterprise linux MITIGATE

Affected: 6.0 · 7.0 · 8.0 · 9.0 · 9.8 · 10.0 · 10.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.0

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.

redhat enterprise linux for els MITIGATE

Affected: 8.10 · 9.8 · 10.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.10

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.

redhat enterprise linux for ibm z systems MITIGATE

Affected: 8.0_s390x · 9.0_s390x · 10.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0_s390x

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

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · selenium-manager · FIXED · 4.45.0-3.fc46 · FEDORA-2026-0af4ceb64a · source

sudo dnf upgrade --advisory=FEDORA-2026-0af4ceb64a

Fedora ELN · libdnf · FIXED · 0.76.0-2.eln159 · FEDORA-2026-dbd263e9d4 · source

sudo dnf upgrade --advisory=FEDORA-2026-dbd263e9d4

Debian 12 · gnutls28 · FIXED · 3.7.9-2+deb12u7

sudo apt update && sudo apt install --only-upgrade gnutls28 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' gnutls28)" ge "3.7.9-2+deb12u7" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · gnutls28 · FIXED · 3.8.9-3+deb13u4

sudo apt update && sudo apt install --only-upgrade gnutls28 dpkg --compare-versions "$(dpkg-query -W -f='${Version}' gnutls28)" ge "3.8.9-3+deb13u4" && echo PATCHED || echo STILL-VULNERABLE

RHEL 10 · gnutls · FIXED · gnutls-3.8.10-4.el10_2

sudo dnf upgrade --advisory=RHSA-2026:20613 rpm -q gnutls

RHEL 10.0 Extended Update Support · gnutls · FIXED · gnutls-3.8.9-9.el10_0.19

sudo dnf upgrade --advisory=RHSA-2026:26409 rpm -q gnutls

RHEL 7 Extended Lifecycle Support · gnutls · FIXED · gnutls-3.3.29-9.el7_9.1

sudo dnf upgrade --advisory=RHSA-2026:34372 rpm -q gnutls

RHEL 8 · gnutls · FIXED · gnutls-3.6.16-8.el8_10.6

sudo dnf upgrade --advisory=RHSA-2026:20611 rpm -q gnutls

RHEL 8.4 Advanced Mission Critical Update Support · gnutls · FIXED · gnutls-3.6.14-10.el8_4.1

sudo dnf upgrade --advisory=RHSA-2026:33125 rpm -q gnutls

Alpine 3.20 · gnutls · FIXED · gnutls-3.8.13-r0

apk add --upgrade gnutls apk info -v gnutls

Alpine 3.21 · gnutls · FIXED · gnutls-3.8.13-r0

apk add --upgrade gnutls apk info -v gnutls

Alpine 3.22 · gnutls · FIXED · gnutls-3.8.13-r0

apk add --upgrade gnutls apk info -v gnutls

Alpine 3.23 · gnutls · FIXED · gnutls-3.8.13-r0

apk add --upgrade gnutls apk info -v gnutls

Amazon Linux 2023 · see advisory · FIXED · ALAS2023-2026-1757 · source

sudo dnf update --advisory=ALAS2023-2026-1757

Amazon Linux 2 · see advisory · FIXED · ALAS2-2026-3324 · source

sudo yum update --advisory=ALAS2-2026-3324

Advisories and coverage

Official advisories

AlmaLinux Errata: [ALSA-2026:20612] Important: gnutls security update 2026-07-02

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-2026-42009?

gnutls: mitigate or apply the listed mitigation; hardened images: mitigate or apply the listed mitigation; openshift container platform: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-42009 being exploited?

CVE-2026-42009 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-2026-42009 affect?

CVE-2026-42009 affects gnutls, hardened images, openshift container platform. Severity is high (CVSS 7.5). A flaw was found in gnutls. A remote attacker could exploit an issue in the Datagram Transport Layer Security (DTLS) packet reordering logic. The comparator function, responsible for ordering DTLS packets by sequence numbers, did not correc

How urgent is CVE-2026-42009?

Priority 54/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Red Hat OpenShift vulnerabilities · GnuTLS vulnerabilities

Related CVEs

CVE-2026-33845 HIGH 7.5 MITIGATE DOWNGRADE A flaw in GnuTLS DTLS handshake parsing allows malformed fragments with zero length and non-zero offset, leadi
CVE-2026-42010 HIGH 7.1 MITIGATE MITIGATE A flaw was found in gnutls
CVE-2026-1584 HIGH 7.5 MITIGATE MITIGATE A flaw was found in gnutls
CVE-2026-3833 MEDIUM 6.5 MITIGATE MITIGATE A flaw was found in gnutls
CVE-2026-3832 LOW 3.7 MITIGATE MITIGATE A flaw was found in gnutls

References

← Back to latest CVEs