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

What is CVE-2025-27936?

CVE-2025-27936 is a medium-severity vulnerability in Mattermost Mattermost Server, published on 16 Apr 2025. Any signed-in user can exploit it over the network, with no action from the victim.

Official 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.

Weakness: CWE-208

Which versions are affected by CVE-2025-27936?

11 open source packages ship an affected version, including github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost-plugin-msteams and github.com/mattermost/mattermost-server. It affects 2 products.

Products include Mattermost Mattermost Server, Mattermost Ms Teams.

How do I fix CVE-2025-27936?

Upgrade github.com/mattermost/mattermost/server/v8 to a fixed version for your release line: 8.0.0-20250218121836-2b5275d87136, 8.0.0-20250314142426-c049748b8863 or 10.5.2.

Is CVE-2025-27936 being exploited?

There is no known exploitation of CVE-2025-27936 in the wild and no public exploit code.

Other vulnerabilities in Mattermost Mattermost Server

• CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers Critical 9.9
• CVE-2025-12421 Account Takeover via Code Exchange Endpoint Critical 9.9
• CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User Critical 9.9
• CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards Critical 9.9
• CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive Critical 9.9

All Mattermost Mattermost Server vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-2j87-p623-8cc2, GO-2025-3618.