{"id":"GHSA-xvcx-mgpc-5xh3","summary":"Mattermost doesn't validate the X-Requested-With header on the 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":["CVE-2026-6339","GO-2026-5769"],"modified":"2026-06-25T23:11:20.374911067Z","published":"2026-05-18T09:31:48Z","database_specific":{"github_reviewed_at":"2026-06-01T15:22:30Z","nvd_published_at":"2026-05-18T09:16:23Z","cwe_ids":["CWE-346"],"severity":"MODERATE","github_reviewed":true},"references":[{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-6339"},{"type":"WEB","url":"https://github.com/mattermost/mattermost/commit/7a339a6438f5a4a5feba6b8de887f17a1378b207"},{"type":"PACKAGE","url":"https://github.com/mattermost/mattermost"},{"type":"WEB","url":"https://mattermost.com/security-updates"}],"affected":[{"package":{"name":"github.com/mattermost/mattermost/server/v8","ecosystem":"Go","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8"},"ranges":[{"type":"SEMVER","events":[{"introduced":"11.5.0"},{"fixed":"11.5.2"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-xvcx-mgpc-5xh3/GHSA-xvcx-mgpc-5xh3.json"}},{"package":{"name":"github.com/mattermost/mattermost/server/v8","ecosystem":"Go","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8"},"ranges":[{"type":"SEMVER","events":[{"introduced":"11.4.0"},{"fixed":"11.4.4"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-xvcx-mgpc-5xh3/GHSA-xvcx-mgpc-5xh3.json"}},{"package":{"name":"github.com/mattermost/mattermost/server/v8","ecosystem":"Go","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"8.0.0-20260327001745-7a339a6438f5"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-xvcx-mgpc-5xh3/GHSA-xvcx-mgpc-5xh3.json"}},{"package":{"name":"github.com/mattermost/mattermost-server","ecosystem":"Go","purl":"pkg:golang/github.com/mattermost/mattermost-server"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"5.3.2-0.20260327001745-7a339a6438f5"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/05/GHSA-xvcx-mgpc-5xh3/GHSA-xvcx-mgpc-5xh3.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L"}]}