YouTube Onebox susceptible to XSS

published 2021-07-15 5 y ago modified 2026-09-10 59 d ago also BIT-discourse-2021-32764 , EUVD-2021-19532 , GHSA-9x4c-29xg-56hw

cvss: 8.1; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.5%; EPSS 0.5% chance of exploitation in 30 days, percentile 45%
public exploits: 0; none known

Discourse is an open-source discussion platform. In Discourse versions 2.7.5 and prior, parsing and rendering of YouTube Oneboxes can be susceptible to XSS attacks. This vulnerability only affects sites which have modified or disabled Discourse's default Content Security Policy. The issue is patched in `stable` version 2.7.6, `beta` version 2.8.0.beta3, and `tests-passed` version 2.8.0.beta3. As a workaround, ensure that the Content Security Policy is enabled, and has not been modified in a way which would make it more vulnerable to XSS attacks.

Exploit prediction

0.55% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	8.1	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
NVD	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
NVD	2.0	3.5	AV:N/AC:M/Au:S/C:N/I:P/A:N
OSV	3.1	8.1	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Affected packages

ecosystem	package	affected	fixed in
bitnami	discourse	<=2.7.5	no fix listed

Affected products

discourse discourse

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

github.com /discourse/discourse/security/advisories/GHSA-9x4c-29xg-56hw
third-party-advisory, advisory
nvd.nist.gov /vuln/detail/CVE-2021-32764
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.

Summary