CVE-2026-27166

EUVD-2026-13187
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.
Basic XSS
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTPrimary
4.1 MEDIUM
NETWORK
LOW
LOW
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N
GitHub_MCNA
4.1 MEDIUM
NETWORK
LOW
LOW
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N
Base Score
CVSS 3.x
EPSS Score
Percentile: Unknown
Affected Products (NVD)
VendorProductVersion
discoursediscourse
𝑥
< 2026.3.0
discoursediscourse
2026.1.0 ≤
𝑥
< 2026.1.2
discoursediscourse
2026.2.0 ≤
𝑥
< 2026.2.1
discoursediscourse
2026.3.0
𝑥
= Vulnerable software versions
Common Weakness Enumeration
References
https://github.com/discourse/discourse/commit/c4762a4fac2f61f52f325396b11d3aeb955ea925
https://github.com/discourse/discourse/security/advisories/GHSA-h653-cq78-vjj2