http4k ReverseProxy Host Header Injection Vulnerability Fix Details

Vulnerability Key Information Summary Vulnerability Overview Vulnerability Type: Reverse Proxy Host Matching Logic Flaw (Reverse Proxy Host Matching Vulnerability) Description: This vulnerability concerns the host header matching logic in Reverse Proxy when processing requests. The original code used the method for host matching, which allows attackers to bypass security restrictions and perform Host Header Injection attacks by constructing specific Host headers (e.g., ). Root Cause: Use of for fuzzy matching instead of exact matching Attackers can exploit substring matching characteristics to embed malicious domains within legitimate domain names Impact Scope Affected Component: reverse proxy module Affected Files: - - - Related test files Affected Versions: Versions using the matching logic Remediation Core Fix Change the host matching method from (substring match) to (exact match): Code Change Details 1. ReverseProxy.kt 2. Test File Updates Security Recommendations 1. Always use exact matching: In production environments, reverse proxy host matching should use the mode. 2. Avoid fuzzy matching: Do not use fuzzy matching methods such as or for security-sensitive host validation. 3. Add input validation: Perform strict format validation and domain whitelist checks on the Host header. 4. Monitor anomalous requests: Monitor requests with Host headers containing anomalous substrings. POC/Exploit Code Summary This fix effectively prevents reverse proxy bypass attacks based on Host Header Injection by enforcing exact matching ( ) instead of fuzzy matching ( ). It is recommended that all systems utilizing reverse proxy features adopt exact matching strategies and collaborate with other security measures (such as IP whitelisting and request signing) to build a defense-in-depth architecture.

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http4k ReverseProxy Host Header Injection Vulnerability Fix Details

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