CVE-2026-35091: A flaw was found in Corosync

This week

HIGH 8.2REMOTEWATCHLISTMITIGATEDOWNGRADEMITIGATE

CVE-2026-35091 is a high-severity flaw (CVSS 8.2) affecting corosync, openshift, enterprise linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A flaw was found in Corosync. A remote unauthenticated attacker can exploit a wrong return value vulnerability in the Corosync membership commit token sanity check by sending a specially crafted User Datagram Protocol (UDP) packet. This can lead to an out-of-bounds read, causing a denial of service (DoS) and potentially disclosing limited memory contents

Why this priority

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

A fixed release or distro patch exists.

Risk facts

CVSS score	8.2 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.9% (top 42%)
CISA exploited list	No
Weakness	CWE-253
Published	2026-04-01
Last modified	2026-10-26

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

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

Am I affected?

Timeline

2026-04-01 14:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

corosync corosync 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 corosync || rpm -q corosync || corosync --version

No fixed or unaffected release known

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

redhat openshift 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 || rpm -q openshift || openshift --version

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

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

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

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

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: 7.0 · 8.0 · 9.0 · 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 7.0

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.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora ELN · openbao · FIXED · 2.6.5-1.eln159 · FEDORA-2026-77adf886ae · source

sudo dnf upgrade --advisory=FEDORA-2026-77adf886ae

Fedora 46 · sugar-turtleart · FIXED · 220-16.fc46 · FEDORA-2026-b79483c788 · source

sudo dnf upgrade --advisory=FEDORA-2026-b79483c788

Debian 12 · corosync · FIXED · 3.1.7-1+deb12u2

sudo apt update && sudo apt install --only-upgrade corosync dpkg --compare-versions "$(dpkg-query -W -f='${Version}' corosync)" ge "3.1.7-1+deb12u2" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · corosync · FIXED · 3.1.9-2+deb13u1

sudo apt update && sudo apt install --only-upgrade corosync dpkg --compare-versions "$(dpkg-query -W -f='${Version}' corosync)" ge "3.1.9-2+deb13u1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 10 · corosync · FIXED · corosync-3.1.9-2.el10_1.1

sudo dnf upgrade --advisory=RHSA-2026:13644 rpm -q corosync

RHEL 10.0 Extended Update Support · corosync · FIXED · corosync-3.1.9-1.el10_0.2

sudo dnf upgrade --advisory=RHSA-2026:14205 rpm -q corosync

RHEL 7 Extended Lifecycle Support · corosync · FIXED · corosync-2.4.5-7.el7_9.3

sudo dnf upgrade --advisory=RHSA-2026:20916 rpm -q corosync

RHEL 8 · corosync · FIXED · corosync-3.1.8-1.el8_10.1

sudo dnf upgrade --advisory=RHSA-2026:13657 rpm -q corosync

RHEL 8.4 Advanced Mission Critical Update Support · corosync · FIXED · corosync-3.1.0-3.el8_4.2

sudo dnf upgrade --advisory=RHSA-2026:14215 rpm -q corosync

Amazon Linux 2023 · see advisory · FIXED · ALAS2023-2026-1560 · source

sudo dnf update --advisory=ALAS2023-2026-1560

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: bugzilla.redhat.com/show_bug.cgi?id=2453169

Advisories and coverage

Official advisories

AlmaLinux Errata: [ALSA-2026:19200] Moderate: corosync security update 2026-06-23

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-2026-35091?

corosync: mitigate or apply the listed mitigation; openshift: downgrade or apply the listed mitigation; enterprise linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-35091 being exploited?

CVE-2026-35091 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-2026-35091 affect?

CVE-2026-35091 affects corosync, openshift, enterprise linux. Severity is high (CVSS 8.2). A flaw was found in Corosync. A remote unauthenticated attacker can exploit a wrong return value vulnerability in the Corosync membership commit token sanity check by sending a specially crafted User Datagram Protocol (UDP) packet. This can

How urgent is CVE-2026-35091?

Priority 58/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Red Hat OpenShift vulnerabilities

Related CVEs

CVE-2026-35092 HIGH 7.5 MITIGATE DOWNGRADE A flaw was found in Corosync

References

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