CVE-2026-19867 — Uncapped mention keys in user notification properties allow CPU exhaustion during post processing

Description (CNA)

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

Affected (CNA)

Vendor / product	Versions
Mattermost / Mattermost	affected 11.10.0 through 11.10.0; affected 11.9.0 through 11.9.1; affected 11.8.0 through 11.8.5; affected 11.7.0 through 11.7.10; unaffected 11.11.0; unaffected 11.10.1; unaffected 11.9.2; unaffected 11.8.6; unaffected 11.7.11

CWE

CWE-770

References

https://mattermost.com/security-updates

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.