Remote Code Execution in Puma Web Server

Executive Summary

CVE-2026-68006 is an HTTP Request Smuggling vulnerability in Puma, a Ruby web server. It occurs because Puma converts underscores in header names to commas, creating mismatches between how front-end proxies and Puma interpret requests. Attackers exploit this by sending headers like Transfer_Encoding or Content_Length, causing Puma to misread request boundaries and enabling attacks such as web cache poisoning or session hijacking.

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Detection Guidance

To detect this vulnerability, inspect HTTP requests for underscore headers like Transfer_Encoding or Content_Length. Use tools like tcpdump or Wireshark to capture and analyze traffic for non-standard header formats. Check proxy logs for inconsistencies between front-end and backend server interpretations of headers.

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Impact Analysis

This vulnerability can lead to serious security issues like web cache poisoning, access control bypass, session hijacking, and sensitive data disclosure. Attackers may manipulate requests to bypass security controls or steal user sessions by exploiting how Puma processes malformed headers.

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Mitigation Strategies

Upgrade Puma to version 8.0.3 or later. Configure front-end proxies to reject requests with underscore headers. Implement input validation to block headers containing underscores. Review and update request parsing logic to handle comma-separated keys correctly.

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