CVE-2026-91123

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the iframe src traversal guard did not treat literal backslashes as path separators after decoded dot segments. A crafted source could therefore pass an allowed_iframes subpath check while browser URL normalization moved the iframe outside the intended allowed path. The resulting iframe could load content from a location that the administrator did not allow. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

• https://github.com/discourse/discourse/commit/042d7b159beda4f74d23e245e8b2e396d9ff8318
• https://github.com/discourse/discourse/commit/097ce5600a2d74d9c68e57974597ab2684bd2a24
• https://github.com/discourse/discourse/commit/0b5a27e689925edce9ba9b14110022435d2b94be
• https://github.com/discourse/discourse/commit/142f5155ad8e56ddb8012c4e70c69a03dedc0579
• https://github.com/discourse/discourse/pull/42882
• https://github.com/discourse/discourse/security/advisories/GHSA-6pwj-wgg8-4rjc