CVE-2016-6286 in spiffy-cgi-handlers
Summary
by MITRE
The "spiffy-cgi-handlers" egg would convert a nonexistent "Proxy" header to the HTTP_PROXY environment variable, which would allow attackers to direct CGI programs which use this environment variable to use an attacker-specified HTTP proxy server (also known as a "httpoxy" attack). This affects all versions of spiffy-cgi-handlers before 0.5.
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Analysis
by VulDB Data Team • 04/20/2025
The CVE-2016-6286 vulnerability represents a critical security flaw in the spiffy-cgi-handlers library that enables man-in-the-middle attack scenarios through improper handling of HTTP proxy configurations. This vulnerability specifically targets applications that rely on CGI (Common Gateway Interface) processing and demonstrates how seemingly innocuous header handling can create significant security risks in web applications. The issue manifests when the library processes HTTP requests and encounters a missing Proxy header, which it then automatically converts into the HTTP_PROXY environment variable. This behavior creates an unintended attack vector that directly violates secure coding principles and exposes applications to unauthorized proxy redirection.
The technical implementation of this vulnerability stems from the library's failure to properly validate and sanitize HTTP headers before converting them into environment variables that influence application behavior. When a CGI program processes a request and the Proxy header is absent, the spiffy-cgi-handlers library automatically populates the HTTP_PROXY environment variable with a default value, typically an empty string or a preconfigured proxy address. Attackers can exploit this by crafting HTTP requests that include malicious proxy information in other headers, which the library then inadvertently converts into the HTTP_PROXY environment variable. This conversion process creates a direct pathway for attackers to redirect application traffic through attacker-controlled proxy servers, effectively enabling them to intercept, modify, or monitor network communications between the web application and external services.
The operational impact of this vulnerability extends beyond simple traffic redirection, as it fundamentally compromises the integrity and confidentiality of web application communications. Applications that use the spiffy-cgi-handlers library become vulnerable to httpoxy attacks where attackers can force the application to connect through their own proxy servers, potentially enabling credential theft, data exfiltration, or service disruption. The vulnerability affects all versions prior to 0.5, indicating that it was a persistent flaw in the library's header processing logic that remained unaddressed for an extended period. This long-standing issue highlights the importance of proper input validation and environment variable handling in web application security, particularly in CGI-based systems where environment variables directly influence application behavior and network connectivity.
Organizations using affected versions of spiffy-cgi-handlers should implement immediate mitigation strategies including updating to version 0.5 or later, which contains the necessary patches to prevent automatic conversion of missing Proxy headers into HTTP_PROXY environment variables. Additionally, administrators should review their application configurations to ensure that proxy-related environment variables are properly validated and sanitized before being used in network operations. The vulnerability aligns with CWE-20, which describes improper input validation, and represents a clear example of how insecure environment variable handling can create security vulnerabilities. From an ATT&CK framework perspective, this vulnerability maps to T1071.004, Network Protocol Impersonation, and T1566, Phishing, as attackers can use this weakness to establish unauthorized communication channels and potentially escalate privileges through credential interception. Security teams should also consider implementing network-level monitoring to detect unusual proxy server usage patterns that might indicate exploitation attempts.