Mattermost Plugins <=2.3.1 DOS via Unrestricted /lifecycle Webhook Body Size
CVE-2026-21388 Published on April 9, 2026
Unbounded Request Body Read in MS Teams Plugin {{/lifecycle}} Webhook Endpoint
Mattermost Plugins versions <=2.3.1 fail to limit the request body size on the {{/lifecycle}} webhook endpoint which allows an authenticated attacker to cause memory exhaustion and denial of service via sending an oversized JSON payload. Mattermost Advisory ID: MMSA-2026-00610
Vulnerability Analysis
CVE-2026-21388 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a small impact on availability.
Weakness Type
Allocation of Resources Without Limits or Throttling
The software allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor.
Products Associated with CVE-2026-21388
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Affected Versions
Mattermost:- Before and including 2.3.1 is affected.
- Version 2.3.2.0 is unaffected.