{"id":"CVE-2026-91134","state":"PUBLISHED","title":"Discourse: Block post iframes whose encoded userinfo bypasses the allowed_iframes allowlist","description":"Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the Discourse post sanitizer allowed a stored cross-origin iframe to bypass the allowed_iframes prefix policy when the iframe src contained encoded userinfo. The sanitizer validated a decoded form differently from the stored iframe src, allowing the browser to interpret an attacker-controlled host while the allowlist check accepted the encoded URL as an allowed prefix. An authenticated user with posting privileges could persist the iframe in a post and cause attacker-controlled cross-origin content to be rendered. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.","publishedAt":"2026-09-24T16:51:34.057Z","updatedAt":"2026-09-29T02:56:30.376Z","severity":{"score":5.4,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["discourse discourse"],"affected":[{"vendor":"discourse","product":"discourse","versions":[{"version":"< 2026.8.0","status":"affected"},{"version":">= 2026.7.0-latest, < 2026.7.2","status":"affected"},{"version":">= 2026.6.0-latest, < 2026.6.3","status":"affected"},{"version":">= 2026.1.0-latest, < 2026.1.8","status":"affected"}]}],"references":["https://github.com/discourse/discourse/security/advisories/GHSA-54vw-chv3-wjpv","https://github.com/discourse/discourse/pull/42882","https://github.com/discourse/discourse/commit/0a8015e6c7a5079981843721494d30c9a91f5415","https://github.com/discourse/discourse/commit/1304b0c04f87534053b0d574ae5a9b9ba13dd590","https://github.com/discourse/discourse/commit/bac7dd1201911851462483271b4567246fa1309d","https://github.com/discourse/discourse/commit/fed3a58c48412ce7207b72a4629ddbc44482cd64"],"weaknesses":["CWE-20"],"ingestedAt":"2026-10-29T20:13:34.582Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/91xxx/CVE-2026-91134.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-91134","state":"PUBLISHED","datePublished":"2026-09-24T16:51:34.057Z","dateUpdated":"2026-09-29T02:56:30.376Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-09-14T19:36:48.844Z"},"containers":{"cna":{"title":"Discourse: Block post iframes whose encoded userinfo bypasses the allowed_iframes allowlist","descriptions":[{"lang":"en","value":"Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the Discourse post sanitizer allowed a stored cross-origin iframe to bypass the allowed_iframes prefix policy when the iframe src contained encoded userinfo. The sanitizer validated a decoded form differently from the stored iframe src, allowing the browser to interpret an attacker-controlled host while the allowlist check accepted the encoded URL as an allowed prefix. An authenticated user with posting privileges could persist the iframe in a post and cause attacker-controlled cross-origin content to be rendered. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0."}],"affected":[{"vendor":"discourse","product":"discourse","versions":[{"version":"< 2026.8.0","status":"affected"},{"version":">= 2026.7.0-latest, < 2026.7.2","status":"affected"},{"version":">= 2026.6.0-latest, < 2026.6.3","status":"affected"},{"version":">= 2026.1.0-latest, < 2026.1.8","status":"affected"}]}],"references":[{"url":"https://github.com/discourse/discourse/security/advisories/GHSA-54vw-chv3-wjpv","name":"https://github.com/discourse/discourse/security/advisories/GHSA-54vw-chv3-wjpv","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/discourse/discourse/pull/42882","name":"https://github.com/discourse/discourse/pull/42882","tags":["x_refsource_MISC"]},{"url":"https://github.com/discourse/discourse/commit/0a8015e6c7a5079981843721494d30c9a91f5415","name":"https://github.com/discourse/discourse/commit/0a8015e6c7a5079981843721494d30c9a91f5415","tags":["x_refsource_MISC"]},{"url":"https://github.com/discourse/discourse/commit/1304b0c04f87534053b0d574ae5a9b9ba13dd590","name":"https://github.com/discourse/discourse/commit/1304b0c04f87534053b0d574ae5a9b9ba13dd590","tags":["x_refsource_MISC"]},{"url":"https://github.com/discourse/discourse/commit/bac7dd1201911851462483271b4567246fa1309d","name":"https://github.com/discourse/discourse/commit/bac7dd1201911851462483271b4567246fa1309d","tags":["x_refsource_MISC"]},{"url":"https://github.com/discourse/discourse/commit/fed3a58c48412ce7207b72a4629ddbc44482cd64","name":"https://github.com/discourse/discourse/commit/fed3a58c48412ce7207b72a4629ddbc44482cd64","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":5.4,"baseSeverity":"MEDIUM","confidentialityImpact":"LOW","integrityImpact":"LOW","privilegesRequired":"LOW","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-20","lang":"en","description":"CWE-20: Improper Input Validation","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-09-24T16:51:34.057Z"},"source":{"advisory":"GHSA-54vw-chv3-wjpv","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-29T02:56:20.350456Z","id":"CVE-2026-91134","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-29T02:56:30.376Z"}}]}}}