Discourse: Onebox iframe origin allowlist enforces URL authority boundary

published 2026-08-10 2 mo ago modified 2026-09-08 2 mo ago also BIT-discourse-2026-72728 , EUVD-2026-55667 , GHSA-qp9j-3v7r-wrvr

cvss: 6.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 24%
public exploits: 0; none known

Discourse is an open-source discussion platform. Prior to 2026.1.7, an authenticated user could submit specially formed URLs that bypassed the Onebox allowlist and embedded malicious content in a site. This issue is fixed in versions 2026.1.7, 2026.6.2, 2026.7.1, and 2026.8.0-latest.1.

Patch / fix

fixed in 2 links 1

bitnami discourse 2026.1.7, 2026.6.2, 2026.7.1
discourse discourse 2026.1.7, 2026.6.2, 2026.7.1, 2026.8.0-latest.1

github.com/discourse/discourse@92eec47 commit

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 2 mo ago (2026-08-10)

Exploit prediction

0.31% chance of exploitation in the next 30 days, higher than 24% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	6.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
OSV	3.1	6.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L

Affected packages

ecosystem	package	affected	fixed in
bitnami	discourse	<2026.1.7 >=2026.6.0, <2026.6.2 >=2026.7.0, <2026.7.1	2026.1.7 2026.6.2 2026.7.1

Affected products

discourse discourse

Classification

Weakness

CWE-20 Improper Input Validation

References

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