CVE-2026-113721: CWE-59: Improper Link Resolution Before File Access ('Link Following') in pypa virtualenv

The vulnerability in virtualenv versions before 21.14.9 arises because ViaTemplateActivator._generate() only removes existing output if Path.exists() returns true, allowing dangling symlinks to persist and redirect activation content generation. Additionally, PyEnvCfg.write() opens pyvenv.cfg without replacing existing symbolic or hard links first. This improper handling of symbolic and hard links (CWE-59) enables a local user who can prepare entries inside the destination directory to cause files outside the requested environment tree to be created or overwritten with virtualenv-generated content, using the invoking user's permissions. The issue requires that the destination parent directory remains controlled by the environment owner during creation. The vulnerability is fixed in version 21.14.9.

A local attacker with limited privileges can exploit this vulnerability to create or overwrite files outside the intended virtual environment directory, potentially leading to unauthorized file modification or privilege escalation within the scope of the invoking user's permissions. The impact includes limited confidentiality, integrity, and availability loss as indicated by the CVSS score of 4.5.

This vulnerability is fixed in virtualenv version 21.14.9. Users should upgrade to version 21.14.9 or later to remediate the issue. No additional mitigation is required if the environment owner controls the destination parent directory during environment creation.