CVE-2026-19867

Uncapped mention keys in user notification properties allow CPU exhaustion during post processing

State: Published
Severity: 4.3 Medium
Published: Oct 16, 2026
Updated: Oct 16, 2026
Reserved: Aug 14, 2026

Description

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

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

References

MMSA-2026-00773vendor-advisory

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