CVE-2026-95666

Unbounded post ID array in the bulk reactions endpoint allows denial of service

State: Published
Severity: 4.3 Medium
Published: Sep 22, 2026
Updated: Sep 22, 2026
Reserved: Sep 22, 2026

Description

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

Scores

CVSS	Score	Vector	Source
3.1	4.3 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L	Mattermost

Weaknesses

CWE-770 Allocation of Resources Without Limits or Throttling

Affected Products

Product	Versions
MattermostMattermost	11.9.0 through 11.9.1Affected 11.8.0 through 11.8.5Affected 11.7.0 through 11.7.10Affected 11.10.0 through 11.10.1Affected 11.11.0Not affected 11.9.2Not affected 11.8.6Not affected 11.7.11Not affected 11.10.2Not affected

References

MMSA-2026-00771vendor-advisory

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