CVE-2015-20107 in Python
Summary
by MITRE • 04/13/2022
In Python (aka CPython) up to 3.10.8, the mailcap module does not add escape characters into commands discovered in the system mailcap file. This may allow attackers to inject shell commands into applications that call mailcap.findmatch with untrusted input (if they lack validation of user-provided filenames or arguments). The fix is also back-ported to 3.7, 3.8, 3.9
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Analysis
by VulDB Data Team • 11/04/2025
The vulnerability identified as CVE-2015-20107 resides within the mailcap module of Python implementations, specifically affecting versions up to 3.10.8. This issue represents a command injection flaw that stems from insufficient sanitization of command strings retrieved from system mailcap files. The mailcap module serves as a mechanism for associating file types with applications that can handle them, commonly used in email clients and other applications that process various file formats. When applications utilize mailcap.findmatch with untrusted input, particularly user-provided filenames or arguments, the lack of proper escaping in command execution creates a significant security risk.
The technical flaw manifests in the mailcap module's failure to properly escape special characters in commands extracted from mailcap configuration files. This oversight allows attackers to manipulate the mailcap entries by injecting malicious shell commands through carefully crafted filenames or arguments. When the vulnerable application processes these untrusted inputs through mailcap.findmatch, the system executes the malicious commands with the privileges of the running application. The vulnerability is particularly dangerous because it leverages the legitimate mailcap functionality to bypass normal input validation mechanisms, making it difficult to detect and prevent through standard security controls.
The operational impact of this vulnerability extends beyond simple command execution, as it can enable attackers to perform arbitrary code execution on systems running vulnerable Python versions. Attackers can exploit this weakness by creating specially crafted filenames or arguments that, when processed through the mailcap module, result in unintended command execution. This could lead to complete system compromise, data exfiltration, or further lateral movement within a network. The vulnerability affects applications that rely on mailcap for file type handling, which includes various email processing systems, file managers, and content delivery applications that have not implemented proper input validation.
Mitigation strategies for CVE-2015-20107 focus on both immediate patching and defensive programming practices. The primary solution involves upgrading to Python versions 3.7.13, 3.8.10, 3.9.7, or 3.10.9, where the vulnerability has been addressed through proper escaping of command characters. Organizations should prioritize patching their Python installations to prevent exploitation of this vulnerability. Additionally, applications should implement proper input validation and sanitization before passing user-provided data to mailcap.findmatch functions. Security practitioners should consider implementing application whitelisting, input filtering, and privilege separation techniques to minimize the impact if exploitation occurs. The vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in OS commands, and can be mapped to ATT&CK technique T1059.001 for command and scripting interpreter. Organizations should also monitor for potential exploitation attempts through unusual mailcap-related system calls or unexpected command executions in their security monitoring systems.