CVE-2026-102937 in virtualenv
Summary
by MITRE • 09/30/2026
virtualenv is a tool for creating isolated virtual python environments. Prior to 21.7.12, BatchActivator.quote() returns prompt text unchanged before activate.bat inserts it into a cmd.exe set "VAR=value" statement. An attacker who influences --prompt, VIRTUALENV_PROMPT, or the corresponding configuration value can include a double quote that closes the assignment and leaves following cmd.exe operators as executable syntax. When a user activates the generated Windows environment, the injected commands run with that user's privileges. This issue is fixed in version 21.7.12.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified in virtualenv versions prior to 21.7.12 represents a critical command injection flaw within the BatchActivator component on Windows systems. Virtualenv is widely used by developers and operations teams to create isolated Python environments, ensuring dependency isolation across different projects. The core of this issue lies in how the tool generates activation scripts for Command Prompt (cmd.exe). Specifically, the BatchActivator.quote() function is responsible for sanitizing input strings before they are embedded into shell commands. In affected versions, this function fails to properly escape double quotes when processing prompt text configurations such as --prompt, VIRTUALENV_PROMPT, or corresponding configuration file values. This lack of proper escaping allows an attacker who controls these inputs to inject malicious syntax directly into the generated activation script.
The technical mechanism of exploitation relies on the structure of Windows batch files and cmd.exe variable assignment statements. When a virtual environment is activated, the tool generates a BatchActivator script that sets various environment variables using the set command in the format set VAR=value. The vulnerability arises because the quote function returns prompt text unchanged if it contains specific characters without adequate escaping. An attacker can craft an input string containing a double quote character followed by additional commands. When this malicious input is processed, the unescaped double quote closes the initial assignment statement prematurely. This structural break causes cmd.exe to interpret any subsequent content in the line not as part of the variable value but as executable command syntax. Consequently, arbitrary operating system commands are executed within the context of the user who runs the activation script.
The operational impact of this vulnerability is severe due to its potential for privilege escalation and unauthorized code execution. Since the injection occurs during the environment activation process, any user or automated system that activates a compromised virtual environment will inadvertently execute the injected payload with their current privileges. This can lead to data exfiltration, installation of malware, pivoting within a network if the victim has broader access rights, or complete compromise of the host machine depending on the context in which the virtualenv is used. The risk is particularly high in shared development environments, continuous integration pipelines, or automated deployment scripts where environment configurations might be dynamically generated based on external inputs that are not sufficiently validated.
This vulnerability aligns with CWE-78 Improper Neutralization of Special Elements used in an OS Command commonly known as OS Command Injection. It also maps to MITRE ATT&CK technique T1059 Command and Scripting Interpreter, specifically sub-techniques related to Windows command shell abuse such as T1059.003 or general script execution patterns like T1204 User Execution if the activation is triggered by social engineering. The flaw highlights a common pitfall in security-focused tool development where input sanitization for one context (Python strings) does not adequately account for the syntactic requirements of another context (Windows batch files).
To mitigate this vulnerability, organizations must ensure that all instances of virtualenv are upgraded to version 21.7.12 or later, which includes a fix for the BatchActivator.quote() function to properly escape double quotes and other special characters before embedding them into activation scripts. For environments where immediate upgrading is not feasible, administrators should enforce strict validation on any inputs that configure VIRTUALENV_PROMPT or similar settings, ensuring they do not contain shell metacharacters such as double quotes, semicolons, or ampersands. Additionally, implementing least-privilege principles for user accounts running development tools can limit the blast radius of a successful exploitation attempt by restricting the permissions available to the injected commands. Regular auditing of third-party dependencies and their configuration inputs is essential to prevent similar injection flaws in other parts of the software supply chain.