CVE-2026-34835
MEDIUMRack: `Rack::Request` accepts invalid Host characters, enabling host allowlist bypass.
Title source: cnaExploitation Summary
EIP tracks 1 public exploit for CVE-2026-34835. PoCs published by Cyber-note.
AI-analyzed exploit summary This repository provides a detailed black-box security analysis of CVE-2026-34835, a Host header validation bypass in Rack. It documents observable behavior, testing methodologies, and potential security impacts without including exploit code or source code review.
Description
Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6, Rack::Request parses the Host header using an AUTHORITY regular expression that accepts characters not permitted in RFC-compliant hostnames, including /, ?, #, and @. Because req.host returns the full parsed value, applications that validate hosts using naive prefix or suffix checks can be bypassed. This can lead to host header poisoning in applications that use req.host, req.url, or req.base_url for link generation, redirects, or origin validation. This issue has been patched in versions 3.1.21 and 3.2.6.
Exploits (1)
This repository provides a detailed black-box security analysis of CVE-2026-34835, a Host header validation bypass in Rack. It documents observable behavior, testing methodologies, and potential security impacts without including exploit code or source code review.
References (1)
Scores
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N