Cross-site scripting in Discourse - CVE-2025-48877
Published: June 9, 2025 / Updated: July 1, 2026
Vulnerability identifier: #VU136107
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:U/U:Clear
CVE-ID: CVE-2025-48877
CWE-ID: CWE-79
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Civilized Discourse Construction Kit, Inc.
Affected software:
Discourse
Discourse
Detailed vulnerability description
The vulnerability allows a remote user to execute arbitrary JavaScript in the iframe scope.
The vulnerability exists due to improper neutralization of active content in embedded CodePen iframe handling when rendering user-supplied embedded CodePen content. A remote user can include a crafted CodePen embed to execute arbitrary JavaScript in the iframe scope.
The issue is related to CodePen being present in the default allowed_iframes site setting.
How to mitigate CVE-2025-48877
Install security update from vendor's website.