Vulnerability · Published Mar 19, 2026 · Assigned by GitHub_M

CVE-2026-27166Discourse vulnerable to HTML injection via prohibited iframe URLs

Medium 4.1

In plain English

A medium-severity security flaw in discourse from discourse. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 10% of all known vulnerabilities).

Severity (CVSS 3.1)4.1Medium

Exploit odds (30 days)0.2%top 90.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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.

Affected products (as reported)

Vendor	Product	Versions
discourse	discourse	< 2026.3.0-latest.1>= 2026.2.0-latest, < 2026.2.1>= 2026.1.0-latest, < 2026.1.2

Weakness: CWE-80 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N

References

https://github.com/discourse/discourse/security/advisories/GHSA-h653-cq78-vjj2 x_refsource_CONFIRM
https://github.com/discourse/discourse/commit/c4762a4fac2f61f52f325396b11d3aeb955ea925 x_refsource_MISC