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.

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact Low

Integrity Impact Low

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
discourse discourse affected
Version Status Constraints
< 2026.8.0 affected —
>= 2026.7.0-latest, < 2026.7.2 affected —
>= 2026.6.0-latest, < 2026.6.3 affected —
>= 2026.1.0-latest, < 2026.1.8 affected —

No data.

No data.

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Vendors Products
Discourse Subscribe
Discourse Subscribe

Project Subscriptions

Vendors Products
Discourse Subscribe
Discourse Subscribe
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/discourse/discourse/commit/0a8015e6c7a5079981843721494d30c9a91f5415 cve-icon cve-icon
https://github.com/discourse/discourse/commit/1304b0c04f87534053b0d574ae5a9b9ba13dd590 cve-icon cve-icon
https://github.com/discourse/discourse/commit/bac7dd1201911851462483271b4567246fa1309d cve-icon cve-icon
https://github.com/discourse/discourse/commit/fed3a58c48412ce7207b72a4629ddbc44482cd64 cve-icon cve-icon
https://github.com/discourse/discourse/pull/42882 cve-icon cve-icon
https://github.com/discourse/discourse/security/advisories/GHSA-54vw-chv3-wjpv cve-icon cve-icon
History

Thu, 24 Sep 2026 19:30:00 +0000

Type Values Removed Values Added
First Time appeared Discourse
Discourse discourse
Vendors & Products Discourse
Discourse discourse

Thu, 24 Sep 2026 17:00:00 +0000

Type Values Removed Values Added
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.
Title Discourse: Block post iframes whose encoded userinfo bypasses the allowed_iframes allowlist
Weaknesses CWE-20
References
Metrics cvssV3_1

{'score': 5.4, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-09-24T16:51:34.057Z

Reserved: 2026-09-14T19:36:48.844Z

Link: CVE-2026-91134

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Deferred

Published: 2026-09-24T17:17:09.080

Modified: 2026-09-24T17:17:09.220

Link: CVE-2026-91134

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-24T19:15:15Z

Weaknesses