CVE-2026-16044: Insufficient validation of guest board admin privileges on archive import

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-17 · updated 2026-08-18
Weakness: CWE-863

Description

Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21 fail to prevent guest users from receiving Board Admin privileges during board archive import which allows a board member to escalate a guest user to Board Admin via importing a crafted .boardarchive file. Mattermost Advisory ID: MMSA-2026-00672

Affected products

Mattermost: from 10.11.0 before 10.11.22; from 11.7.0 before 11.7.7 — fixed in 10.11.22, 11.7.7

How to fix

Upgrade to a fixed version: Mattermost 10.11.22, 11.7.7. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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