{"id":"CVE-2026-12985","state":"PUBLISHED","title":"Mattermost DCR redirect URI allowlist bypass via improper URL component validation","description":"Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 Mattermost failed to validate Dynamic Client Registration redirect URIs by URL component (matching glob patterns against the raw URI string instead) which allows a remote unauthenticated attacker to register an OAuth client with an attacker-controlled callback host that bypasses the configured redirect URI allowlist via a crafted redirect URI that places an allowlisted host/path suffix inside the query string.. Mattermost Advisory ID: MMSA-2026-00700","publishedAt":"2026-09-14T14:09:53.799Z","updatedAt":"2026-09-15T03:56:02.615Z","severity":{"score":6.8,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N","source":"Mattermost"},"assigner":"Mattermost","products":["Mattermost Mattermost"],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.9.0","status":"affected","lessThanOrEqual":"11.9.0","versionType":"semver"},{"version":"11.8.0","status":"affected","lessThanOrEqual":"11.8.4","versionType":"semver"},{"version":"11.7.0","status":"affected","lessThanOrEqual":"11.7.7","versionType":"semver"},{"version":"11.10.0","status":"unaffected"},{"version":"11.9.1","status":"unaffected"},{"version":"11.8.5","status":"unaffected"},{"version":"11.7.8","status":"unaffected"}]}],"references":["https://mattermost.com/security-updates"],"weaknesses":["CWE-601"],"ingestedAt":"2026-10-29T20:10:52.580Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/12xxx/CVE-2026-12985.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-12985","state":"PUBLISHED","datePublished":"2026-09-14T14:09:53.799Z","dateUpdated":"2026-09-15T03:56:02.615Z","assignerShortName":"Mattermost","assignerOrgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateReserved":"2026-06-23T11:43:37.353Z"},"containers":{"cna":{"title":"Mattermost DCR redirect URI allowlist bypass via improper URL component validation","descriptions":[{"lang":"en","value":"Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 Mattermost failed to validate Dynamic Client Registration redirect URIs by URL component (matching glob patterns against the raw URI string instead) which allows a remote unauthenticated attacker to register an OAuth client with an attacker-controlled callback host that bypasses the configured redirect URI allowlist via a crafted redirect URI that places an allowlisted host/path suffix inside the query string.. Mattermost Advisory ID: MMSA-2026-00700"}],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.9.0","status":"affected","lessThanOrEqual":"11.9.0","versionType":"semver"},{"version":"11.8.0","status":"affected","lessThanOrEqual":"11.8.4","versionType":"semver"},{"version":"11.7.0","status":"affected","lessThanOrEqual":"11.7.7","versionType":"semver"},{"version":"11.10.0","status":"unaffected"},{"version":"11.9.1","status":"unaffected"},{"version":"11.8.5","status":"unaffected"},{"version":"11.7.8","status":"unaffected"}]}],"references":[{"url":"https://mattermost.com/security-updates","name":"MMSA-2026-00700","tags":["vendor-advisory"]}],"metrics":[{"cvssV3_1":{"attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"REQUIRED","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"NONE","version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N","baseSeverity":"MEDIUM","baseScore":6.8},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-601","lang":"en","type":"CWE","description":"CWE-601: URL Redirection to Untrusted Site (“Open Redirect”)"}]}],"providerMetadata":{"shortName":"Mattermost","orgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateUpdated":"2026-09-14T14:09:53.799Z"},"credits":[{"lang":"en","type":"finder","value":"aryangurjarf401a3"}],"solutions":[{"value":"Update Mattermost to versions 11.10.0, 11.9.1, 11.8.5, 11.7.8 or higher.","lang":"en"}],"source":{"advisory":"MMSA-2026-00700","defect":["https://mattermost.atlassian.net/browse/MM-69360"],"discovery":"EXTERNAL"},"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-14T00:00:00+00:00","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3","id":"CVE-2026-12985"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-15T03:56:02.615Z"}}]}}}