CVE-2026-113726: virtualenv activate runs commands from the environment name in zsh with PROMPT_SUBST

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-20 · updated 2026-10-27
Weakness: CWE-78

Description

virtualenv is a tool for creating isolated virtual python environments. Prior to 21.13.0, the bash activate script that zsh also sources leaves the environment name unescaped; from 21.13.0 until 21.14.4, it escapes backslashes, dollar signs, and backticks only when BASH_VERSION is set, so zsh receives the raw value. The script assigns that value to PS1. In zsh with PROMPT_SUBST, an attacker-influenced environment directory, --prompt, or VIRTUALENV_PROMPT value containing command, parameter, or arithmetic expansion syntax can therefore execute commands in the user's shell each time the prompt is drawn. A percent sign is separately interpreted as a zsh prompt escape but does not by itself execute commands. Plain zsh with PROMPT_SUBST disabled and bash are not affected by this mechanism. This issue is fixed in version 21.14.4.

Affected products

Pypi Virtualenv: before 21.14.4; 0.8, 0.8.1, 0.8.2, 0.8.3, 0.8.4, 0.9 (+293) — fixed in 21.14.4
pypa virtualenv: before 21.14.4

How to fix

Upgrade to a fixed version: Pypi Virtualenv 21.14.4. Check the vendor advisory for mitigations.

References

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