CVE-2026-2457 WebSocket Message Spoofing via Permalink Embed Manipulation

What is CVE-2026-2457?

CVE-2026-2457 is a medium-severity vulnerability in Mattermost Mattermost Server, published on 16 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to sanitize client-supplied post metadata which allows an authenticated attacker to spoof permalink embeds impersonating other users via crafted PUT requests to the post update API endpoint.. Mattermost Advisory ID: MMSA-2025-00569

Weakness: CWE-346

Which versions are affected by CVE-2026-2457?

14 open source packages ship an affected version, including github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server/v5 and github.com/mattermost/mattermost-server/v6. It affects 1 product.

Products include Mattermost Mattermost Server.

How do I fix CVE-2026-2457?

Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 5.3.2-0.20260123211116-9efe617be8b8, 10.11.11, 10.11.11+incompatible or 11.2.3+incompatible.

Is CVE-2026-2457 being exploited?

There is no known exploitation of CVE-2026-2457 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-ph22-fw5m-w2q9, GO-2026-4732.