{"cve":"CVE-2026-6339","nvd":{"published":"2026-05-18T09:16:23.573","modified":"2026-10-14T20:10:00.190","status":"Analyzed","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","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N","score":4.3},"cwes":["CWE-346"],"references":["https://mattermost.com/security-updates"],"products":["mattermost:mattermost_server"],"source":"nvd","synced_at":"2026-10-19T22:35:16.954578616+00:00"},"epss":{"cve":"CVE-2026-6339","score":0.00113,"percentile":0.01393,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-xvcx-mgpc-5xh3","url":"https://osv.dev/vulnerability/GHSA-xvcx-mgpc-5xh3","summary":"Mattermost doesn't validate the X-Requested-With header on the burn-on-read reveal endpoint","modified":"2026-06-25T23:11:08.526631477Z","packages":[{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","ranges":[">=11.5.0 <11.5.2"],"fixed":["11.5.2"]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","ranges":[">=11.4.0 <11.4.4"],"fixed":["11.4.4"]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","ranges":["<8.0.0-20260327001745-7a339a6438f5"],"fixed":["8.0.0-20260327001745-7a339a6438f5"]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","ranges":["<5.3.2-0.20260327001745-7a339a6438f5"],"fixed":["5.3.2-0.20260327001745-7a339a6438f5"]}]},{"id":"GO-2026-5769","url":"https://osv.dev/vulnerability/GO-2026-5769","summary":"Mattermost doesn't validate the X-Requested-With header on the burn-on-read reveal endpoint in github.com/mattermost/mattermost-server","modified":"2026-06-25T23:01:41.269315004Z","packages":[{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","ranges":[">=11.4.0+incompatible <11.4.4+incompatible",">=11.5.0+incompatible <11.5.2+incompatible"],"fixed":["11.4.4+incompatible","11.5.2+incompatible"]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server/v5","purl":"pkg:golang/github.com/mattermost/mattermost-server/v5","ranges":["all versions"],"fixed":[]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server/v6","purl":"pkg:golang/github.com/mattermost/mattermost-server/v6","ranges":["all versions"],"fixed":[]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","ranges":["<8.0.0-20260327001745-7a339a6438f5"],"fixed":["8.0.0-20260327001745-7a339a6438f5"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}