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CVE-2026-3109: Mattermost Plugins versions <=11.4 10.11.11.0 fail to validate webhook request timestamps which allows an atta

13
Routine
LOW 2.2UPGRADE

CVE-2026-3109 is a low-severity flaw (CVSS 2.2) affecting mattermost server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Mattermost Plugins versions <=11.4 10.11.11.0 fail to validate webhook request timestamps which allows an attacker to corrupt Zoom meeting state in Mattermost via replayed webhook requests. Mattermost Advisory ID: MMSA-2026-00584

Why this priority

  • No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score2.2 (Low)
Attack vectorNetwork (remote)
Attack complexityHigh
Privileges neededHigh
User interactionNone
EPSS exploit chance0.3% (top 77%)
CISA exploited listNo
WeaknessCWE-754
Published2026-03-26
Last modified2026-06-17
Publisher (CNA): Mattermost, Inc. · Vendor: mattermost

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Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

mattermost mattermost server UPGRADE
Affected: >= 10.11.0 and < 10.11.12
Fixed in: 10.11.12
Safe to downgrade to: a release before 10.11.0
1. Check installed version
apt-cache policy mattermost-server || rpm -q mattermost-server || mattermost-server --version
2. UPGRADE to 10.11.12 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade mattermost-server
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade mattermost-server
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
3. If no update is available yet, DOWNGRADE to a release before 10.11.0 (Debian / Ubuntu)
apt-cache madison mattermost-server sudo apt install mattermost-server=<VERSION_BEFORE_10.11.0> sudo apt-mark hold mattermost-server
3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list mattermost-server sudo dnf downgrade mattermost-server-<VERSION_BEFORE_10.11.0> sudo dnf versionlock add mattermost-server
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.
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-2026-3109?

mattermost server: upgrade to 10.11.12. Exact commands for each OS are on this page.

Is CVE-2026-3109 being exploited?

CVE-2026-3109 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-2026-3109 affect?

CVE-2026-3109 affects mattermost server. Severity is low (CVSS 2.2). Mattermost Plugins versions <=11.4 10.11.11.0 fail to validate webhook request timestamps which allows an attacker to corrupt Zoom meeting state in Mattermost via replayed webhook requests. Mattermost Advisory ID: MMSA-2026-00584

How urgent is CVE-2026-3109?

Priority 13/100. No elevated risk signals yet.

Software pages

Zoom vulnerabilities · Mattermost vulnerabilities

Related CVEs

References

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