{"id":"CVE-2026-6339","state":"PUBLISHED","title":"Missing request origin validation on burn-on-read reveal endpoint","description":"Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636","publishedAt":"2026-05-18T08:05:30.925Z","updatedAt":"2026-05-18T12:42:01.321Z","severity":{"score":4.3,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","source":"Mattermost"},"assigner":"Mattermost","products":["Mattermost Mattermost"],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.5.0","status":"affected","lessThanOrEqual":"11.5.1","versionType":"semver"},{"version":"11.4.0","status":"affected","lessThanOrEqual":"11.4.3","versionType":"semver"},{"version":"11.6.0","status":"unaffected"},{"version":"11.5.2","status":"unaffected"},{"version":"11.4.4","status":"unaffected"}]}],"references":["https://mattermost.com/security-updates"],"weaknesses":["CWE-346"],"ingestedAt":"2026-10-29T20:12:49.727Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/6xxx/CVE-2026-6339.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-6339","state":"PUBLISHED","datePublished":"2026-05-18T08:05:30.925Z","dateUpdated":"2026-05-18T12:42:01.321Z","assignerShortName":"Mattermost","assignerOrgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateReserved":"2026-04-15T10:27:52.835Z"},"containers":{"cna":{"title":"Missing request origin validation on burn-on-read reveal endpoint","descriptions":[{"lang":"en","value":"Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636"}],"affected":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.5.0","status":"affected","lessThanOrEqual":"11.5.1","versionType":"semver"},{"version":"11.4.0","status":"affected","lessThanOrEqual":"11.4.3","versionType":"semver"},{"version":"11.6.0","status":"unaffected"},{"version":"11.5.2","status":"unaffected"},{"version":"11.4.4","status":"unaffected"}]}],"references":[{"url":"https://mattermost.com/security-updates","name":"MMSA-2026-00636","tags":["vendor-advisory"]}],"metrics":[{"cvssV3_1":{"attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"LOW","version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","baseSeverity":"MEDIUM","baseScore":4.3},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-346","lang":"en","type":"CWE","description":"CWE-346: Origin Validation Error"}]}],"providerMetadata":{"shortName":"Mattermost","orgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","dateUpdated":"2026-05-18T08:05:30.925Z"},"credits":[{"lang":"en","type":"finder","value":"game0v3r"}],"solutions":[{"value":"Update Mattermost to versions 11.6.0, 11.5.2, 11.4.4 or higher.","lang":"en"}],"source":{"advisory":"MMSA-2026-00636","defect":["https://mattermost.atlassian.net/browse/MM-68000"],"discovery":"EXTERNAL"},"x_generator":{"engine":"cvelib 1.8.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-05-18T12:41:50.625706Z","id":"CVE-2026-6339","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":"2026-05-18T12:42:01.321Z"}}]}}}