{"id":"CVE-2026-19603","state":"PUBLISHED","title":"Private channel ID disclosure via user status endpoints","description":"Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765","publishedAt":"2026-10-16T07:02:38.486Z","updatedAt":"2026-10-16T11:59:09.985Z","severity":{"score":4.3,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N","source":"Mattermost"},"assigner":"Mattermost","products":["Mattermost Mattermost"],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.9.0","status":"affected","lessThanOrEqual":"11.9.1","versionType":"semver"},{"version":"11.8.0","status":"affected","lessThanOrEqual":"11.8.5","versionType":"semver"},{"version":"11.7.0","status":"affected","lessThanOrEqual":"11.7.10","versionType":"semver"},{"version":"11.10.0","status":"affected","lessThanOrEqual":"11.10.1","versionType":"semver"},{"version":"11.11.0","status":"unaffected"},{"version":"11.9.2","status":"unaffected"},{"version":"11.8.6","status":"unaffected"},{"version":"11.7.11","status":"unaffected"},{"version":"11.10.2","status":"unaffected"}]}],"references":["https://mattermost.com/security-updates"],"weaknesses":["CWE-201"],"ingestedAt":"2026-10-29T20:11:10.572Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/19xxx/CVE-2026-19603.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-19603","state":"PUBLISHED","datePublished":"2026-10-16T07:02:38.486Z","dateUpdated":"2026-10-16T11:59:09.985Z","assignerShortName":"Mattermost","assignerOrgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateReserved":"2026-08-12T07:34:04.177Z"},"containers":{"cna":{"title":"Private channel ID disclosure via user status endpoints","descriptions":[{"lang":"en","value":"Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765"}],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.9.0","status":"affected","lessThanOrEqual":"11.9.1","versionType":"semver"},{"version":"11.8.0","status":"affected","lessThanOrEqual":"11.8.5","versionType":"semver"},{"version":"11.7.0","status":"affected","lessThanOrEqual":"11.7.10","versionType":"semver"},{"version":"11.10.0","status":"affected","lessThanOrEqual":"11.10.1","versionType":"semver"},{"version":"11.11.0","status":"unaffected"},{"version":"11.9.2","status":"unaffected"},{"version":"11.8.6","status":"unaffected"},{"version":"11.7.11","status":"unaffected"},{"version":"11.10.2","status":"unaffected"}]}],"references":[{"url":"https://mattermost.com/security-updates","name":"MMSA-2026-00765","tags":["vendor-advisory"]}],"metrics":[{"cvssV3_1":{"attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"NONE","availabilityImpact":"NONE","version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N","baseSeverity":"MEDIUM","baseScore":4.3},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-201","lang":"en","type":"CWE","description":"CWE-201: Insertion of Sensitive Information Into Sent Data"}]}],"providerMetadata":{"shortName":"Mattermost","orgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateUpdated":"2026-10-16T07:02:38.486Z"},"credits":[{"lang":"en","type":"finder","value":"CERT PL"}],"solutions":[{"value":"Update Mattermost to versions 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2 or higher.","lang":"en"}],"source":{"advisory":"MMSA-2026-00765","defect":["https://mattermost.atlassian.net/browse/MM-70215"],"discovery":"EXTERNAL"},"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-16T11:58:53.325388Z","id":"CVE-2026-19603","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T11:59:09.985Z"}}]}}}