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CVE PROGRAM SOURCE RECORD5.4 Medium

CVE-2026-91134

Discourse: Block post iframes whose encoded userinfo bypasses the allowed_iframes allowlist

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Status
Published
Published
Updated
Assigning organization
GitHub_M

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.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

discourse discourse

  • < 2026.8.0affected
  • >= 2026.7.0-latest, < 2026.7.2affected
  • >= 2026.6.0-latest, < 2026.6.3affected
  • >= 2026.1.0-latest, < 2026.1.8affected

References