What is CVE-2026-95666?

CVE-2026-95666 is a medium-severity vulnerability in Mattermost, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 4.3/10. Published 2026-09-22.

How severe is CVE-2026-95666?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Resource exhaustion in Mattermost

CVE-2026-95666

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

Published 2026-09-22 · last modified 2026-09-22.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Mattermost

Weakness classification (CWE)

CWE-770 — Allocation of Resources Without Limits or Throttling

References

mattermost.com/security-updates (vendor-advisory)

Frequently asked questions

What is CVE-2026-95666?: CVE-2026-95666 is a medium-severity vulnerability in Mattermost, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 4.3/10. Published 2026-09-22.
How severe is CVE-2026-95666?: Medium severity. CVSS v3 base score is 4.3 out of 10.