Discourse IFRAME redirect via Codepen in v<2026.3.0-latest.1
CVE-2026-27166 Published on March 19, 2026
Discourse vulnerable to HTML injection via prohibited iframe URLs
Discourse is an open source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1 and 2026.1.2, insufficient cleanup in the default Codepen allowed iframes value allows an attacker to trick a user into changing the URL of the main page. This issue has been fixed in versions 2026.3.0-latest.1, 2026.2.1 and 2026.1.2. To workaround this issue, remove Codepen from the list of allowed iframes.
Vulnerability Analysis
CVE-2026-27166 is exploitable with network access, requires user interaction and a small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, with no impact on integrity, and no impact on availability.
Weakness Type
What is a Basic XSS Vulnerability?
The software receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages. This may allow such characters to be treated as control characters, which are executed client-side in the context of the user's session. Although this can be classified as an injection problem, the more pertinent issue is the improper conversion of such special characters to respective context-appropriate entities before displaying them to the user.
CVE-2026-27166 has been classified to as a Basic XSS vulnerability or weakness.
Products Associated with CVE-2026-27166
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Affected Versions
discourse:- Version < 2026.3.0-latest.1 is affected.
- Version >= 2026.2.0-latest, < 2026.2.1 is affected.
- Version >= 2026.1.0-latest, < 2026.1.2 is affected.