CVE-2025-27936: Webhook Secret Exposure via Timing attack in MSteams plugin

Severity: medium (CVSS 5.9 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: 2025-04-16 · updated 2026-06-17
Weakness: CWE-208

Description

Mattermost Plugin MSTeams versions <2.1.0 and Mattermost Server versions 10.5.x <=10.5.1 with the MS Teams plugin enabled fail to perform constant time comparison on a MSTeams plugin webhook secret which allows an attacker to retrieve the webhook secret of the MSTeams plugin via a timing attack during webhook secret comparison.

Affected products

Mattermost: before 10.5.2 — fixed in 10.5.2
Mattermost Ms Teams: before 2.1.0 — fixed in 2.1.0

How to fix

Upgrade to a fixed version: Mattermost 10.5.2; Mattermost Ms Teams 2.1.0. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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