CVE-2016-1000110 in Python
Summary
by MITRE
The CGIHandler class in Python before 2.7.12 does not protect against the HTTP_PROXY variable name clash in a CGI script, which could allow a remote attacker to redirect HTTP requests.
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Analysis
by VulDB Data Team • 09/26/2024
The vulnerability identified as CVE-2016-1000110 resides within the CGIHandler class implementation in Python versions prior to 2.7.12, representing a critical security flaw that undermines the integrity of HTTP request handling in CGI environments. This issue stems from the improper management of environment variables, specifically the HTTP_PROXY variable, which creates a dangerous conflict when CGI scripts execute within Python's web server framework. The vulnerability manifests when a CGI script processes HTTP requests and inadvertently inherits or modifies the HTTP_PROXY environment variable, leading to potential redirection of traffic through unauthorized proxy servers.
The technical flaw operates through a fundamental lack of environment variable sanitization within the CGIHandler class, which fails to properly isolate or validate the HTTP_PROXY variable during script execution. When a web application processes a CGI request, the Python interpreter passes through environment variables including HTTP_PROXY, which may contain proxy server information that could be exploited by malicious actors. The absence of proper validation mechanisms means that an attacker can manipulate this variable to redirect HTTP traffic through their own proxy servers, potentially intercepting sensitive data or routing requests through compromised infrastructure.
This vulnerability presents significant operational impact within web server environments that rely on Python's CGI capabilities for dynamic content generation. Remote attackers can exploit this flaw to perform man-in-the-middle attacks, redirect traffic to malicious endpoints, or potentially gain unauthorized access to internal network resources that would otherwise be protected by proxy configurations. The implications extend beyond simple traffic redirection as the flaw can enable more sophisticated attacks including credential theft, data exfiltration, and network reconnaissance activities that leverage the compromised proxy routing mechanisms.
The vulnerability aligns with CWE-200, which addresses improper handling of environment variables, and represents a specific instance of insecure coding practices in web application frameworks. From an ATT&CK perspective, this weakness maps to T1071.004 for application layer protocol manipulation and T1041 for data encryption for exfiltration, as attackers can leverage the proxy variable manipulation to redirect and potentially compromise network traffic. Organizations using Python versions before 2.7.12 in CGI environments face heightened risk of unauthorized network access and data interception attacks that exploit this fundamental flaw in environment variable handling.
Mitigation strategies should prioritize immediate patching of affected Python installations to version 2.7.12 or later, where the CGIHandler class properly sanitizes environment variables including HTTP_PROXY. Additionally, organizations should implement strict environment variable validation at the application level, deploy network monitoring solutions to detect anomalous proxy traffic patterns, and consider implementing additional security controls such as reverse proxy configurations that explicitly handle and validate proxy-related environment variables. Security teams should also conduct comprehensive vulnerability assessments to identify any CGI scripts that may be running in affected environments and ensure proper input validation and environment variable isolation practices are implemented across all web application frameworks.