CVE-2026-113721: virtualenv: Generated files can follow existing destination links

Severity: medium (CVSS 4.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-20 · updated 2026-10-28
Weakness: CWE-59

Description

virtualenv is a tool for creating isolated virtual python environments. Prior to 21.14.9, ViaTemplateActivator._generate() removes an existing output only when Path.exists() is true, allowing a dangling symlink to survive and redirect generated activation content, while PyEnvCfg.write() opens pyvenv.cfg without first replacing an existing symbolic or hard link. Another local account that prepares final entries inside the destination can therefore cause environment creation to create or overwrite files outside the requested tree with constrained virtualenv-generated content and the invoking user's permissions. The destination parent must remain controlled by the environment owner during creation; concurrent parent-directory replacement is a separate concern. This issue is fixed in version 21.14.9.

Affected products

Pypi Virtualenv: before 21.14.9; 0.8, 0.8.1, 0.8.2, 0.8.3, 0.8.4, 0.9 (+298) — fixed in 21.14.9
pypa virtualenv: before 21.14.9

How to fix

Upgrade to a fixed version: Pypi Virtualenv 21.14.9. Check the vendor advisory for mitigations.

References

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