{"id":"CVE-2026-6339","sourceIdentifier":"responsibledisclosure@mattermost.com","published":"2026-05-18T09:16:23.573","lastModified":"2026-10-14T20:10:00.190","vulnStatus":"Analyzed","cveTags":[],"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"},{"lang":"es","value":"Las versiones de Mattermost 11.5.x menor o igual que 11.5.1, 11.4.x menor o igual que 11.4.3 no validan el encabezado X-Requested-With en el endpoint de revelación de mensajes de lectura única, lo que permite a un miembro autenticado del canal forzar la revelación de un mensaje de lectura única sin el consentimiento del destinatario a través de una etiqueta de imagen Markdown manipulada. ID de Aviso de Mattermost: MMSA-2026-00636"}],"affected":[{"source":"responsibledisclosure@mattermost.com","affectedData":[{"vendor":"Mattermost","product":"Mattermost","defaultStatus":"unaffected","versions":[{"version":"11.5.0","lessThanOrEqual":"11.5.1","versionType":"semver","status":"affected"},{"version":"11.4.0","lessThanOrEqual":"11.4.3","versionType":"semver","status":"affected"},{"version":"11.6.0","status":"unaffected"},{"version":"11.5.2","status":"unaffected"},{"version":"11.4.4","status":"unaffected"}]}]}],"metrics":{"cvssMetricV31":[{"source":"responsibledisclosure@mattermost.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","baseScore":4.3,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"NONE","availabilityImpact":"LOW"},"exploitabilityScore":2.8,"impactScore":1.4},{"source":"nvd@nist.gov","type":"Primary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N","baseScore":4.3,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"NONE","availabilityImpact":"NONE"},"exploitabilityScore":2.8,"impactScore":1.4}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-05-18T12:41:50.625706Z","id":"CVE-2026-6339","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"responsibledisclosure@mattermost.com","type":"Secondary","description":[{"lang":"en","value":"CWE-346"}]}],"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*","versionStartIncluding":"11.4.0","versionEndExcluding":"11.4.4","matchCriteriaId":"CF171039-837A-4D23-87EB-F328AD04976C"},{"vulnerable":true,"criteria":"cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*","versionStartIncluding":"11.5.0","versionEndExcluding":"11.5.2","matchCriteriaId":"726AD6AD-6C01-45BB-9115-B8209717A6D4"}]}]}],"references":[{"url":"https://mattermost.com/security-updates","source":"responsibledisclosure@mattermost.com","tags":["Vendor Advisory"]}]}