Is CVE-2026-19867 being exploited?

No public exploit is currently tracked.

How severe is CVE-2026-19867?

CVE-2026-19867 has a CVSS v3 severity of MEDIUM (4.3).

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CVE-2026-19867

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