Discourse up to 2026.1.7/2026.6.2/2026.7.1 Iframe Src Traversal Guard path traversal

Summaryinfo

A vulnerability has been found in Discourse up to 2026.1.7/2026.6.2/2026.7.1 and classified as critical. This vulnerability affects unknown code of the component Iframe Src Traversal Guard. The manipulation leads to path traversal. This vulnerability is listed as CVE-2026-91123. The attack may be initiated remotely. There is no available exploit. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Discourse up to 2026.1.7/2026.6.2/2026.7.1. It has been rated as critical. This issue affects an unknown part of the component Iframe Src Traversal Guard. The manipulation with an unknown input leads to a path traversal vulnerability. Using CWE to declare the problem leads to CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-91123 since 09/14/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1006 according to MITRE ATT&CK.

Upgrading to version 2026.1.8, 2026.6.3, 2026.7.2 or 2026.8.0 eliminates this vulnerability.

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Productinfo

Type

• Chat Software

Name

• Discourse

Version

• 2026.1.0
• 2026.1.1
• 2026.1.2
• 2026.1.3
• 2026.1.4
• 2026.1.5
• 2026.1.6
• 2026.1.7
• 2026.6.0
• 2026.6.1
• 2026.6.2
• 2026.7.0
• 2026.7.1

License

• open-source

Website

• Product: https://github.com/discourse/discourse/

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