CVE-2026-113725 in virtualenv
Summary
by MITRE • 10/20/2026
virtualenv is a tool for creating isolated virtual python environments. Prior to 21.14.7, the bash activate script escapes the environment name for only one of the two passes bash makes over PS1, so a backslash in the name undoes the escaping and a name containing \$(...) runs as commands in the user's shell each time bash draws the prompt. This issue is fixed in version 21.14.7.
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Analysis
by VulDB Data Team • 10/20/2026
The vulnerability identified within virtualenv versions prior to 21.14.7 represents a significant code injection risk stemming from improper handling of environment names during shell initialization. Virtualenv is widely utilized by developers and operations teams to create isolated Python environments, ensuring dependency isolation across different projects. The core issue resides in the bash activation script generated for these virtual environments. When a user activates a virtual environment, the script modifies the PS1 variable, which controls the appearance of the command prompt in interactive shells. This modification is designed to visually indicate that the current shell session is operating within an isolated context by prepending or appending specific text representing the environment name.
The technical flaw arises from how bash processes escape sequences within double-quoted strings assigned to variables like PS1. Bash performs two passes over such strings: first, it interprets and resolves escape characters and variable expansions; second, it stores the resulting string for display. In vulnerable versions of virtualenv, the environment name was escaped only during one of these two processing stages. This incomplete escaping strategy creates a critical gap in security logic. Specifically, if an attacker or a user with malicious intent constructs a virtual environment directory path containing specific shell metacharacters, particularly backslashes followed by dollar signs and parentheses, they can exploit this parsing inconsistency.
The operational impact of this flaw is severe because it leads to arbitrary command execution within the context of the victim's shell session. When bash draws the prompt after activating such a maliciously named environment, the unescaped sequence \$(...) is interpreted as a command substitution operator. Consequently, any commands enclosed within those parentheses are executed immediately by the user's shell before displaying the prompt. This means that if an attacker can trick a developer into creating or switching to a virtual environment with a crafted name, such as one containing backslash-dollar-parenthesis sequences pointing to malicious scripts or payloads, arbitrary code will run on the victim's machine every time the terminal refreshes its display. This effectively bypasses user expectations of isolation and safety associated with using virtual environments for development work.
This vulnerability aligns closely with CWE-94, which describes Improper Control of Generation of Code (Code Injection), as well as CWE-78, the OS Command Injection weakness. From an offensive security perspective, this behavior mirrors techniques found in MITRE ATT&CK framework under command and script interpretation vectors, where attackers leverage legitimate system utilities to execute unauthorized commands. The risk is exacerbated by the fact that virtual environments are often created based on project names or repository paths provided by third parties, CI/CD pipelines, or shared team directories, increasing the attack surface for supply chain-style attacks via malicious environment naming conventions.
Mitigation strategies primarily involve upgrading to version 21.14.7 of virtualenv, where the developers corrected the escaping logic to ensure that both passes performed by bash properly sanitize special characters in the environment name. For organizations unable to upgrade immediately, administrative controls should be implemented to restrict the creation or activation of virtual environments with names containing shell metacharacters such as backslashes, dollar signs, and parentheses. Additionally, security awareness training for development teams can help mitigate social engineering vectors that might lead users to activate untrusted environment configurations. Regular auditing of installed packages and adherence to strict naming conventions for project directories further reduces the likelihood of encountering this specific code injection vector in production or development workflows.