What is CVE-2026-19867?

CVE-2026-19867 is a medium-severity vulnerability in Mattermost, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 4.3/10. Published 2026-10-16.

How severe is CVE-2026-19867?

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

Resource exhaustion in Mattermost

CVE-2026-19867

Mattermost versions 11.10.x <= 11.10.0, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to cap the number and size of mention keys stored in a user's notification properties, and to bound the quadratic multibyte-keyword matching performed for each post, which allows an authenticated user to degrade post-processing latency and consume excessive CPU on behalf of other members of any channel they share via storing an oversized notify_props.mention_keys list on their own profile.. Mattermost Advisory ID: MMSA-2026-00773

Published 2026-10-16 · last modified 2026-10-16.

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-2026-19867?: CVE-2026-19867 is a medium-severity vulnerability in Mattermost, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 4.3/10. Published 2026-10-16.
How severe is CVE-2026-19867?: Medium severity. CVSS v3 base score is 4.3 out of 10.