CVE-2025-55073: MS Teams plugin OAuth allows editing arbitrary posts

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-11-14 · updated 2026-10-19
Weakness: CWE-306

Description

Mattermost versions 10.11.x <= 10.11.3, 10.5.x <= 10.5.11, 10.12.x <= 10.12.0 fail to validate the relationship between the post being updated and the MSTeams plugin OAuth flow which allows an attacker to edit arbitrary posts via a crafted MSTeams plugin OAuth redirect URL.

Affected products

Mattermost: from 10.5.0 before 10.5.12; from 10.11.0 before 10.11.4; from 10.12.0 before 10.12.1 — fixed in 10.11.4, 10.12.1, 10.5.12

How to fix

Upgrade to a fixed version: Mattermost 10.11.4, 10.12.1, 10.5.12. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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