CVE-2026-95666 PUBLISHED

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

Assigner: Mattermost
Reserved: 22.09.2026 Published: 22.09.2026 Updated: 22.09.2026

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

Metrics

CVSS 3.1

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

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	Low	Integrity Impact	None
User Interaction	None	Availability Impact	Low

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.9.0 to 11.9.1 (incl.) affected from 11.8.0 to 11.8.5 (incl.) affected from 11.7.0 to 11.7.10 (incl.) affected from 11.10.0 to 11.10.1 (incl.) 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

Solutions

Update Mattermost to versions 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2 or higher.

Credits

idr finder

References

MMSA-2026-00771

Problem Types

CWE-770: Allocation of Resources Without Limits or Throttling CWE