Discourse vulnerable to HTML injection via prohibited iframe URLs

published 2026-03-19 7 mo ago modified 2026-09-08 2 mo ago also BIT-discourse-2026-27166 , EUVD-2026-13187 , GHSA-h653-cq78-vjj2

cvss: 4.1; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 9%
public exploits: 0; none known

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.

Patch / fix

fixed in 2 links 1

bitnami discourse 2026.1.2, 2026.2.1, 2026.3.0
discourse discourse 2026.1.2, 2026.2.1, 2026.3.0-latest.1

github.com/discourse/discourse@c4762a4 commit

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 7 mo ago (2026-03-21)

Exploit prediction

0.20% chance of exploitation in the next 30 days, higher than 9% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.1	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:L/A:N
NVD	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
OSV	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
bitnami	discourse	>=2026.1.0, <2026.1.2 >=2026.2.0, <2026.2.1 >=2026.3.0, <2026.3.0	2026.1.2 2026.2.1 2026.3.0

Affected products

discourse discourse

Classification

Weakness

CWE-80 Improper Neutralization of Script-Related HTML Tags in a Web Page

References

github.com /discourse/discourse/commit/c4762a4fac2f61f52f325396b11d3aeb955ea925
patch
github.com /discourse/discourse/security/advisories/GHSA-h653-cq78-vjj2
vendor-advisory, advisory
nvd.nist.gov /vuln/detail/CVE-2026-27166
web

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.

Summary