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Vulnerability record · CVE-2026-91123 · published 24 September 2026

CVE-2026-91123: Path traversal vulnerability

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.

7.2 CVSS 3.1 High EPSS 0.29% · top 81.0% CWE-22 · Path traversal Deferred
7.2CVSS 3.1 base score
0.29%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
6References
24 Sep 2026Last modified by NVD

Description

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

References

LinkTags
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

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Source: NIST National Vulnerability Database (record CVE-2026-91123), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.