Vulnerability in Ruby Webrick
CVE-2025-6442
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.
Vulnerability class: HTTP Request Smuggling
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N.
EPSS exploit prediction
EPSS: 0.005 (40.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 40th percentile — 40.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.001
Affected products
- Ruby Webrick — versions 1.8.1
- Ruby-Lang Webrick
Weakness classification (CWE)
Public proof-of-concept exploits
References
- www.zerodayinitiative.com/advisories/ZDI-25-414/ (x_research-advisory, Third Party Advisory)
- github.com/ruby/webrick/commit/ee60354bcb84ec33b9245e1d1aa6e1f7e8132101 (vendor-advisory, Patch)
Frequently asked questions
- What is CVE-2025-6442?
- CVE-2025-6442 is a medium-severity vulnerability in Ruby Webrick, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 5.9/10. Published 2025-06-25.
- How severe is CVE-2025-6442?
- Medium severity. CVSS v3 base score is 5.9 out of 10.
- Is CVE-2025-6442 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.