{"id":"CVE-2026-6339","revision":"6936f61a065c4a278cb36065f940c8ba","records":[{"revision":"6936f61a065c4a278cb36065f940c8ba","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-6339","aliases":[],"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","state":0,"publishedAt":"2026-05-18T08:05:30.925+00:00","modifiedAt":"2026-05-18T12:42:01.321+00:00","affected":[{"ecosystem":"Vendor product","name":"Mattermost","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"defaultStatus\": \"unaffected\",\n                    \"product\": \"Mattermost\",\n                    \"vendor\": \"Mattermost\",\n                    \"versions\": [\n                        {\n                            \"lessThanOrEqual\": \"11.5.1\",\n                            \"status\": \"affected\",\n                            \"version\": \"11.5.0\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"lessThanOrEqual\": \"11.4.3\",\n                            \"status\": \"affected\",\n                            \"version\": \"11.4.0\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"11.6.0\",\n                            \"status\": \"unaffected\"\n                        },\n                        {\n                            \"version\": \"11.5.2\",\n                            \"status\": \"unaffected\"\n                        },\n                        {\n                            \"version\": \"11.4.4\",\n                            \"status\": \"unaffected\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","score":4.3,"severity":"MEDIUM"}],"references":["https://mattermost.com/security-updates"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-6339","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-6339","identifiers":["CVE-2026-6339"]},"retained":false,"historicalAffected":[]}],"coverage":[]}