{"schema":"threatline.record/2","record":{"id":"CVE-2026-18551","aliases":[],"summary":"Mattermost guest account privilege escalation via member roles API","details":"Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate the combination of guest and admin scheme roles which allows an authenticated attacker to escalate a guest account to team or channel admin via a crafted PUT request to the member roles API endpoint.. Mattermost Advisory ID: MMSA-2026-00752","categories":["Applications & CMS"],"product":"Mattermost","vendor":"Mattermost","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-18551","source_modified_at":"2026-10-20T13:11:28.823Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"Mattermost","vendor":"Mattermost","versions":[{"lessThanOrEqual":"11.10.0","status":"affected","version":"11.10.0","versionType":"semver"},{"lessThanOrEqual":"11.7.9","status":"affected","version":"11.7.0","versionType":"semver"},{"lessThanOrEqual":"11.9.1","status":"affected","version":"11.9.0","versionType":"semver"},{"lessThanOrEqual":"11.8.5","status":"affected","version":"11.8.0","versionType":"semver"},{"version":"11.11.0","status":"unaffected"},{"version":"11.10.1","status":"unaffected"},{"version":"11.7.10","status":"unaffected"},{"version":"11.9.2","status":"unaffected"},{"version":"11.8.6","status":"unaffected"}],"defaultStatus":"unaffected"}],"fixed_versions":[],"cvss":6.5,"severity":"Medium","kev":{"listed":false},"epss":{"probability":0.00222,"percentile":0.12117,"score_date":"2026-10-23"},"published_at":"2026-10-16T06:56:51.996Z","modified_at":"2026-10-20T13:11:28.823Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-18551","fetched_at":"2026-10-23T18:45:31.882637Z","source_modified_at":"2026-10-20T13:11:28.823Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-18551","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","EPSS"],"references":[{"source":"CVE List","url":"https://mattermost.com/security-updates","tags":["vendor-advisory"]}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","cvss_source":"CVE List","ssvc":{"exploitation":"none","automatable":"no","technical_impact":"total","assessed_at":"2026-10-17T03:55:37.074789Z"},"classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":"product","confidence":"heuristic","reviewed":false},"change_timestamp":"2026-10-20T13:11:28.823Z","content_hash":"dc35ad4f8d4aae7c827db34b9f61ddad8e1803df2357b389615e1ff95228d45a"}}