CVE-2025-48877: Discourse

Critical severity, CVSS 9.8. EPSS: 0.4% chance of exploitation in the next 30 days.

Discourse is an open-source discussion platform. Prior to version 3.4.4 of the `stable` branch, version 3.5.0.beta5 of the `beta` branch, and version 3.5.0.beta6-dev of the `tests-passed` branch, Codepen is present in the default `allowed_iframes` site setting, and it can potentially auto-run arbitrary JS in the iframe scope, which is unintended. This issue is patched in version 3.4.4 of the `stable` branch, version 3.5.0.beta5 of the `beta` branch, and version 3.5.0.beta6-dev of the `tests-passed` branch. As a workaround, the Codepen prefix can be removed from a site's `allowed_iframes`.

Affected products

• Discourse Discourse: before 3.4.4 (fixed in 3.4.4); before 3.5.0 (fixed in 3.5.0); version 3.5.0 only

Published 2025-06-09. Last modified 2026-06-17.