Medium severity · published Mar 19, 2026
CVE-2026-27166
Discourse vulnerable to HTML injection via prohibited iframe URLs
5.4
CVSS
0.2%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 9% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
DI
discourse · discourse
< 2026.3.0-latest.1; >= 2026.2.0-latest, < 2026.2.1; >= 2026.1.0-latest, < 2026.1.2 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27166
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-27166
Patch
https://github.com/discourse/discourse/commit/c4762a4fac2f61f52f325396b11d3aeb955ea925
Vendor Advisory
https://github.com/discourse/discourse/security/advisories/GHSA-h653-cq78-vjj2
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