CVE-2025-6442: Ruby-Lang Webrick

Medium severity, CVSS 5.9. EPSS: 0.5% chance of exploitation in the next 30 days.

Ruby WEBrick read_header HTTP Request Smuggling Vulnerability. This vulnerability allows remote attackers to smuggle arbitrary HTTP requests on affected installations of Ruby WEBrick. This issue is exploitable when the product is deployed behind an HTTP proxy that fulfills specific conditions. The specific flaw exists within the read_headers method. The issue results from the inconsistent parsing of terminators of HTTP headers. An attacker can leverage this vulnerability to smuggle arbitrary HTTP requests. Was ZDI-CAN-21876.

Affected products

• Ruby-Lang Webrick: before 1.8.2 (fixed in 1.8.2)

Published 2025-06-25. Last modified 2026-06-17.