{"api_version":"1","generated_at":"2026-06-02T17:31:22+00:00","cve":"CVE-2026-6339","urls":{"html":"https://cve.report/CVE-2026-6339","api":"https://cve.report/api/cve/CVE-2026-6339.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-6339","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-6339"},"summary":{"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":"PUBLISHED","assigner":"Mattermost","published_at":"2026-05-18 09:16:23","updated_at":"2026-05-18 19:11:13"},"problem_types":["CWE-346","CWE-346 CWE-346: Origin Validation Error"],"metrics":[{"version":"3.1","source":"nvd@nist.gov","type":"Primary","score":"4.3","severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N","data":{"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"}},{"version":"3.1","source":"responsibledisclosure@mattermost.com","type":"Secondary","score":"4.3","severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","data":{"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"}},{"version":"3.1","source":"CNA","type":"CVSS","score":"4.3","severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","data":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"LOW","baseScore":4.3,"baseSeverity":"MEDIUM","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"LOW","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","version":"3.1"}}],"references":[{"url":"https://mattermost.com/security-updates","name":"https://mattermost.com/security-updates","refsource":"responsibledisclosure@mattermost.com","tags":["Vendor Advisory"],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-6339","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-6339","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Mattermost","product":"Mattermost","version":"affected 11.5.0 11.5.1 semver","platforms":[]},{"source":"CNA","vendor":"Mattermost","product":"Mattermost","version":"affected 11.4.0 11.4.3 semver","platforms":[]},{"source":"CNA","vendor":"Mattermost","product":"Mattermost","version":"unaffected 11.6.0","platforms":[]},{"source":"CNA","vendor":"Mattermost","product":"Mattermost","version":"unaffected 11.5.2","platforms":[]},{"source":"CNA","vendor":"Mattermost","product":"Mattermost","version":"unaffected 11.4.4","platforms":[]}],"timeline":[],"solutions":[{"source":"CNA","title":"","value":"Update Mattermost to versions 11.6.0, 11.5.2, 11.4.4 or higher.","time":"","lang":"en"}],"workarounds":[],"exploits":[],"credits":[{"source":"CNA","value":"game0v3r","lang":"en"}],"nvd_cpes":[{"cve_year":"2026","cve_id":"6339","vulnerable":"1","versionEndIncluding":"","cpe1":"cpe","cpe2":"2.3","cpe3":"a","cpe4":"mattermost","cpe5":"mattermost_server","cpe6":"*","cpe7":"*","cpe8":"*","cpe9":"*","cpe10":"*","cpe11":"*","cpe12":"*","cpe13":"*"}],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"6339","cve":"CVE-2026-6339","epss":"0.000160000","percentile":"0.039600000","score_date":"2026-05-26","updated_at":"2026-05-27 00:01:53"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"adp":[{"metrics":[{"other":{"content":{"id":"CVE-2026-6339","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","timestamp":"2026-05-18T12:41:50.625706Z","version":"2.0.3"},"type":"ssvc"}}],"providerMetadata":{"dateUpdated":"2026-05-18T12:42:01.321Z","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP"},"title":"CISA ADP Vulnrichment"}],"cna":{"affected":[{"defaultStatus":"unaffected","product":"Mattermost","vendor":"Mattermost","versions":[{"lessThanOrEqual":"11.5.1","status":"affected","version":"11.5.0","versionType":"semver"},{"lessThanOrEqual":"11.4.3","status":"affected","version":"11.4.0","versionType":"semver"},{"status":"unaffected","version":"11.6.0"},{"status":"unaffected","version":"11.5.2"},{"status":"unaffected","version":"11.4.4"}]}],"credits":[{"lang":"en","type":"finder","value":"game0v3r"}],"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"}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"LOW","baseScore":4.3,"baseSeverity":"MEDIUM","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"LOW","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L","version":"3.1"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-346","description":"CWE-346: Origin Validation Error","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-05-18T08:05:30.925Z","orgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","shortName":"Mattermost"},"references":[{"name":"MMSA-2026-00636","tags":["vendor-advisory"],"url":"https://mattermost.com/security-updates"}],"solutions":[{"lang":"en","value":"Update Mattermost to versions 11.6.0, 11.5.2, 11.4.4 or higher."}],"source":{"advisory":"MMSA-2026-00636","defect":["https://mattermost.atlassian.net/browse/MM-68000"],"discovery":"EXTERNAL"},"title":"Missing request origin validation on burn-on-read reveal endpoint","x_generator":{"engine":"cvelib 1.8.0"}}},"cveMetadata":{"assignerOrgId":"9302f53e-dde5-4bf3-b2f2-a83f91ac0eee","assignerShortName":"Mattermost","cveId":"CVE-2026-6339","datePublished":"2026-05-18T08:05:30.925Z","dateReserved":"2026-04-15T10:27:52.835Z","dateUpdated":"2026-05-18T12:42:01.321Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-05-18 09:16:23","lastModifiedDate":"2026-05-18 19:11:13","problem_types":["CWE-346","CWE-346 CWE-346: Origin Validation Error"],"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}]},"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"}]}]}]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"6339","Ordinal":"1","Title":"Missing request origin validation on burn-on-read reveal endpoin","CVE":"CVE-2026-6339","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"6339","Ordinal":"1","NoteData":"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","Type":"Description","Title":"Missing request origin validation on burn-on-read reveal endpoin"}]}}}