CVE-2023-29196: HTML injection via topic embedding in Discourse

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-04-18 · updated 2026-06-17
Weakness: CWE-79

Description

Discourse is an open source platform for community discussion. This vulnerability is not exploitable on the default install of Discourse. A custom feature must be enabled for it to work at all, and the attacker’s payload must pass the CSP to be executed. However, if an attacker succeeds in embedding Javascript that does pass the CSP, it could result in session hijacking for any users that view the attacker’s post. The vulnerability is patched in the latest tests-passed, beta and stable branches. Users are advised to upgrade. Users unable to upgrade should enable and/or restore your site's CSP to the default one provided with Discourse. Remove any embed-able hosts configured.

Affected products

discourse: before 3.0.3; before 3.1.0; 3.1.0-beta1, 3.1.0-beta2, 3.1.0-beta3 — fixed in 3.0.3, 3.1.0

How to fix

Upgrade to a fixed version: discourse 3.0.3, 3.1.0. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2023-29196 or the next vulnerability affects your stack