---
id: CVE-2026-91134
title: Discourse is an open-source discussion platform
summary: >-
  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 conta…
severity: medium
cvss: 5.4
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N'
cwe:
  - CWE-20
vendor: discourse
product: discourse
affected:
  - discourse < 2026.8.0
  - 'discourse >= 2026.7.0-latest, < 2026.7.2'
  - 'discourse >= 2026.6.0-latest, < 2026.6.3'
  - 'discourse >= 2026.1.0-latest, < 2026.1.8'
published: '2026-09-24'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T17:17:09.220'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-91134'
references:
  - url: >-
      https://github.com/discourse/discourse/commit/0a8015e6c7a5079981843721494d30c9a91f5415
    label: security-advisories@github.com
  - url: >-
      https://github.com/discourse/discourse/commit/1304b0c04f87534053b0d574ae5a9b9ba13dd590
    label: security-advisories@github.com
  - url: >-
      https://github.com/discourse/discourse/commit/bac7dd1201911851462483271b4567246fa1309d
    label: security-advisories@github.com
  - url: >-
      https://github.com/discourse/discourse/commit/fed3a58c48412ce7207b72a4629ddbc44482cd64
    label: security-advisories@github.com
  - url: 'https://github.com/discourse/discourse/pull/42882'
    label: security-advisories@github.com
  - url: >-
      https://github.com/discourse/discourse/security/advisories/GHSA-54vw-chv3-wjpv
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-24T17:48:30.387Z'
epss: 0.00216
epssPercentile: 0.107
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.