CVE-2011-1015 in Python
Summary
by MITRE
The is_cgi method in CGIHTTPServer.py in the CGIHTTPServer module in Python 2.5, 2.6, and 3.0 allows remote attackers to read script source code via an HTTP GET request that lacks a / (slash) character at the beginning of the URI.
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Analysis
by VulDB Data Team • 11/07/2021
The vulnerability identified as CVE-2011-1015 represents a critical security flaw in Python's CGIHTTPServer module that affects versions 2.5, 2.6, and 3.0. This vulnerability resides in the is_cgi method implementation within the CGIHTTPServer.py file, which serves as a simple HTTP server capable of executing CGI scripts. The flaw stems from inadequate input validation and URI parsing logic that fails to properly handle requests lacking the leading slash character in the URI path. When a remote attacker submits an HTTP GET request without the initial forward slash, the server's parsing mechanism becomes confused and incorrectly processes the request, leading to unintended behavior that exposes sensitive script source code. This vulnerability operates at the application layer and specifically targets the server-side script execution environment, making it particularly dangerous for systems that rely on Python's built-in HTTP server for development or testing purposes.
The technical exploitation of this vulnerability occurs through a carefully crafted HTTP GET request that omits the required leading slash character from the URI. The is_cgi method in CGIHTTPServer.py performs URI path validation and script execution logic that becomes compromised when the slash character is absent. This flaw creates a path traversal condition where the server's internal path resolution mechanism fails to properly sanitize or validate the request path, allowing the attacker to bypass normal script execution boundaries and gain access to the raw source code of CGI scripts. The vulnerability is classified as a path traversal issue that maps to CWE-22, which specifically addresses improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. The attack vector operates through the HTTP protocol and leverages the server's insufficient input validation to manipulate the execution flow of the CGI handler.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with complete access to the source code of CGI scripts running on the affected server. This exposure can reveal sensitive implementation details including database connection strings, API keys, cryptographic secrets, and business logic that could be exploited for further attacks. The vulnerability is particularly concerning in development environments where Python's CGIHTTPServer is used for testing purposes, as these systems often contain incomplete security configurations and may be accessible to untrusted users. The attack can be executed remotely without authentication requirements, making it accessible to any attacker who can reach the vulnerable server. The severity is amplified by the fact that this vulnerability affects multiple Python versions, creating a widespread impact across various deployment environments and potentially compromising numerous development and testing systems.
Mitigation strategies for CVE-2011-1015 involve immediate patching of affected Python installations to versions that contain the corrected CGIHTTPServer implementation. Organizations should implement network segmentation to restrict access to systems running vulnerable Python versions and consider disabling the CGIHTTPServer module entirely in production environments. The recommended approach includes deploying proper input validation mechanisms that enforce strict URI path formatting and implementing access controls that prevent unauthorized access to script execution capabilities. Security measures should also include monitoring for suspicious HTTP requests that lack proper URI formatting and implementing web application firewalls to detect and block malformed requests. From a compliance standpoint, this vulnerability aligns with ATT&CK technique T1566.001 which covers the exploitation of vulnerabilities in web applications, and organizations should ensure their security controls address both the immediate patching requirements and broader application security practices. The vulnerability demonstrates the importance of proper input validation and the principle of least privilege in server configurations, as well as the necessity of regular security assessments to identify and remediate similar issues in custom server implementations.