CVE-2025-6442: ruby-lang webrick HTTP Request/Response Smuggling

Vulnerability summary

CVE-2025-6442 is a medium (CVSS 6.5) HTTP Request/Response Smuggling vulnerability in ruby-lang webrick. EPSS estimates a 0.50% chance of exploitation in the next 30 days, higher than 41.1% of scored vulnerabilities.

Timeline

1. 25-06-2025
   PublishedVulnerability first disclosed.
2. 25-06-2025
   Last modifiedVulnerability information updated.

Description

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.

• CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.