{"id":"CVE-2026-6339","summary":"Missing request origin validation on burn-on-read reveal endpoint","details":"Mattermost versions 11.5.x \u003c= 11.5.1, 11.4.x \u003c= 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","aliases":["GHSA-xvcx-mgpc-5xh3","GO-2026-5769"],"modified":"2026-07-08T08:13:48.541563108Z","published":"2026-05-18T08:05:30.925Z","database_specific":{"cwe_ids":["CWE-346"],"cna_assigner":"Mattermost","unresolved_ranges":[{"source":"AFFECTED_FIELD","extracted_events":[{"introduced":"11.5.0"},{"last_affected":"11.5.1"},{"introduced":"11.4.0"},{"last_affected":"11.4.3"}]}],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/6xxx/CVE-2026-6339.json"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/6xxx/CVE-2026-6339.json"},{"type":"ADVISORY","url":"https://mattermost.com/security-updates"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-6339"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/mattermost/mattermost","events":[{"introduced":"2a1ac98bd3fae587927adf9340ba266c8c02018e"},{"fixed":"37b08cfe7154241c2c6a8af0fd500e0785bbc900"},{"introduced":"9f2616376582893035a7e3cb38b0fab648bba4e8"},{"fixed":"cc4ef6863ee114bc96be4e34478ec2f0db3eac4e"}],"database_specific":{"cpe":"cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*","source":"CPE_RANGE","extracted_events":[{"introduced":"11.4.0"},{"fixed":"11.4.4"},{"introduced":"11.5.0"},{"fixed":"11.5.2"}]}}],"versions":["v11.5.0","v11.5.2-rc2","v11.5.2-rc1","v11.4.3","v11.5.1","v11.4.2","v11.4.1-rc2","v11.4.1-rc1","v11.4.1","v11.4.0-rc3","v11.4.0","mattermost-redux@11.4.0","@mattermost/types@11.4.0","@mattermost/client@11.4.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-6339.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L"}]}