CVE-2026-2578 Information Disclosure via WebSocket Event When Deleting Unrevealed Burn on Read Posts

What is CVE-2026-2578?

CVE-2026-2578 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 fail to preserve the redacted state of burn-on-read posts during deletion which allows channel members to access unrevealed burn-on-read message contents via the WebSocket post deletion event.. Mattermost Advisory ID: MMSA-2026-00579

Weakness: CWE-201

Which versions are affected by CVE-2026-2578?

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-2026-2578?

Upgrade github.com/mattermost/mattermost-server to a fixed version for your release line: 5.3.2-0.20260127062706-c6b205f0d770, 10.11.11, 10.11.11+incompatible or 11.2.3+incompatible.

Is CVE-2026-2578 being exploited?

There is no known exploitation of CVE-2026-2578 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-3rhr-jr63-hwq5, GO-2026-4734.