Mattermost 11.3.x WebSocket Leak Exposes BurnonRead Posts
CVE-2026-2578 Published on March 16, 2026
Information Disclosure via WebSocket Event When Deleting Unrevealed Burn on Read Posts
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
Vulnerability Analysis
CVE-2026-2578 is exploitable with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality, a small impact on integrity and availability.
Weakness Type
Insertion of Sensitive Information Into Sent Data
The code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor. Sensitive information could include data that is sensitive in and of itself (such as credentials or private messages), or otherwise useful in the further exploitation of the system (such as internal file system structure).
Products Associated with CVE-2026-2578
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Affected Versions
Mattermost:- Version 11.3.0, <= 11.3.0 is affected.
- Version 11.4.0 is unaffected.
- Version 11.3.1 is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.