CVE-2026-0998: Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 and Mattermost Plugin Zoom versions

Q: How do I fix CVE-2026-0998?

mattermost server: upgrade to 10.11.10, 11.1.3, 11.2.2; zoom: upgrade to newer than 1.11.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-0998 being exploited?

CVE-2026-0998 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-2026-0998 affect?

CVE-2026-0998 affects mattermost server, zoom. Severity is medium (CVSS 4.3). Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 and Mattermost Plugin Zoom versions <=1.11.0 fail to validate user identity and post ownership in the {{/api/v1/askPMI}} endpoint which allows unauthorized users to

Q: How urgent is CVE-2026-0998?

Priority 17/100. No elevated risk signals yet.

Routine

MEDIUM 4.3UPGRADEUPGRADE

CVE-2026-0998 is a medium-severity flaw (CVSS 4.3) affecting mattermost server, zoom. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 and Mattermost Plugin Zoom versions <=1.11.0 fail to validate user identity and post ownership in the {{/api/v1/askPMI}} endpoint which allows unauthorized users to start Zoom meetings as any user and overwrite arbitrary posts via direct API calls with manipulated user IDs and post data.. Mattermost Advisory ID: MMSA-2025-00534

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 93%)
CISA exploited list	No
Weakness	CWE-862
Published	2026-02-16
Last modified	2026-06-17

Publisher (CNA): Mattermost, Inc. · Vendor: mattermost

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

Am I affected?

Timeline

2026-02-16 10:16 UTCPublished CVE record published
2026-06-17 10:11 UTCUpdated Record last modified

mattermost mattermost server UPGRADE

Affected: >= 10.11.0 and < 10.11.10 · >= 11.1.0 and < 11.1.3 · >= 11.2.0 and < 11.2.2

Fixed in: 10.11.10, 11.1.3, 11.2.2

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 10.11.10 (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.

mattermost zoom UPGRADE

Affected: <= 1.11.0

Fixed in: newer than 1.11.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 1.11.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade zoom

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade zoom

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2026-0998?

mattermost server: upgrade to 10.11.10, 11.1.3, 11.2.2; zoom: upgrade to newer than 1.11.0. Exact commands for each OS are on this page.

Is CVE-2026-0998 being exploited?

CVE-2026-0998 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-2026-0998 affect?

CVE-2026-0998 affects mattermost server, zoom. Severity is medium (CVSS 4.3). Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 and Mattermost Plugin Zoom versions <=1.11.0 fail to validate user identity and post ownership in the {{/api/v1/askPMI}} endpoint which allows unauthorized users to

How urgent is CVE-2026-0998?

Priority 17/100. No elevated risk signals yet.

Software pages

Zoom vulnerabilities · Mattermost vulnerabilities

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References

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