CVE-2026-95666 is a vulnerability in MatterMost
Published on September 22, 2026
Unbounded post ID array in the bulk reactions endpoint allows denial of service
Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771
Vulnerability Analysis
CVE-2026-95666 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 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-2026-95666
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Affected Versions
Mattermost:- Version 11.9.0, <= 11.9.1 is affected.
- Version 11.8.0, <= 11.8.5 is affected.
- Version 11.7.0, <= 11.7.10 is affected.
- Version 11.10.0, <= 11.10.1 is affected.
- Version 11.11.0 is unaffected.
- Version 11.9.2 is unaffected.
- Version 11.8.6 is unaffected.
- Version 11.7.11 is unaffected.
- Version 11.10.2 is unaffected.