CVE-2021-43794: Anonymous user cache poisoning via development-mode header in Discourse

Severity: medium (CVSS 5.0 v2.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-12-01 · updated 2026-06-17
Weakness: CWE-610

Description

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.

Affected products

discourse: before 2.7.11 — fixed in 2.7.11

How to fix

Upgrade to a fixed version: discourse 2.7.11. Check the vendor advisory for mitigations.

References

https://github.com/discourse/discourse/commit/2da0001965c6d8632d723c46ea5df9f22a1a23f1
https://github.com/discourse/discourse/security/advisories/GHSA-249g-pc77-65hp
https://github.com/discourse/discourse/commit/2da0001965c6d8632d723c46ea5df9f22a1a23f1
https://github.com/discourse/discourse/security/advisories/GHSA-249g-pc77-65hp

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