Input validation error in Discourse - CVE-2026-55420
Published: July 1, 2026
Vulnerability identifier: #VU136599
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-55420
CWE-ID: CWE-20
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 code.
The vulnerability exists due to improper input validation in PDF upload processing when handling uploaded PDF files under certain non-default configurations. A remote user can upload a specially crafted PDF file to execute arbitrary code.
Only installations using certain non-default configurations are vulnerable.
How to mitigate CVE-2026-55420
Install security update from vendor's website.