What is CVE-2021-43794?

CVE-2021-43794 is a medium-severity vulnerability in Discourse, classified under Externally Controlled Reference to a Resource in Another Sphere. CVSS score: 5.3/10. Published 2021-12-01.

How severe is CVE-2021-43794?

Medium severity. CVSS v3 base score is 5.3 out of 10.

Vulnerability in Discourse

CVE-2021-43794

Discourse is an open source discussion platform. In affected versions an attacker can poison the cache for anonymous (i.e. not logged in) users, such that the users are shown a JSON blob instead of the HTML page. This can lead to a partial denial-of-service. This issue is patched in the latest stable, beta and tests-passed versions of Discourse.

Published 2021-12-01 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.

EPSS exploit prediction

EPSS: 0.011 (62.9th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 63rd percentile — 62.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.010 · newest: 0.011 · change: +0.000

Affected products

Discourse — versions stable < 2.7.11, beta < 2.8.0.beta9, tests-passed < 2.8.0.beta9

Weakness classification (CWE)

CWE-610 — Externally Controlled Reference to a Resource in Another Sphere

References

github.com/discourse/discourse/commit/2da0001965c6d8632d723c46ea5df9f22a1a23f1 (Patch, Third Party Advisory)
github.com/discourse/discourse/security/advisories/GHSA-249g-pc77-65hp (Third Party Advisory)

Frequently asked questions

What is CVE-2021-43794?: CVE-2021-43794 is a medium-severity vulnerability in Discourse, classified under Externally Controlled Reference to a Resource in Another Sphere. CVSS score: 5.3/10. Published 2021-12-01.
How severe is CVE-2021-43794?: Medium severity. CVSS v3 base score is 5.3 out of 10.