{"id":"CVE-2026-19867","title":"Uncapped mention keys in user notification properties allow CPU exhaustion during post processing","summary":"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 matchi…","severity":"medium","cvss":4.3,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","cvssSource":"cna","cwe":["CWE-770"],"vendor":"Mattermost","product":"Mattermost","affected":["Mattermost >= 11.10.0 <= 11.10.0","Mattermost >= 11.9.0 <= 11.9.1","Mattermost >= 11.8.0 <= 11.8.5","Mattermost >= 11.7.0 <= 11.7.10"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-10-16T11:59:55.782423Z"},"published":"2026-10-16","updated":"2026-10-16","sourceUpdated":"2026-10-16T12:00:11.330Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-19867","references":[{"url":"https://mattermost.com/security-updates","label":"MMSA-2026-00773"}],"tags":["cve.org"],"ingestedAt":"2026-10-16T08:02:23.125Z","slug":"CVE-2026-19867","body":"## Overview\n\nMattermost 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\n\n## Affected\n\n- `Mattermost >= 11.10.0 <= 11.10.0`\n- `Mattermost >= 11.9.0 <= 11.9.1`\n- `Mattermost >= 11.8.0 <= 11.8.5`\n- `Mattermost >= 11.7.0 <= 11.7.10`\n\n## Remediation\n\nUpdate Mattermost to versions 11.11.0, 11.10.1, 11.9.2, 11.8.6, 11.7.11 or higher.","depth":"sunlit","depthScore":24,"depthScoreParts":{"impact":23.7,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}