CVE-2026-102938: virtualenv writes prompt values into pyvenv.cfg without sanitizing line boundaries, allowing configuration injection

Severity: medium (CVSS 5.8 v4.0)
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: 2026-09-29 · updated 2026-09-30
Weakness: CWE-93

Description

virtualenv is a tool for creating isolated virtual python environments. Prior to 21.7.11, PyEnvCfg.write() writes prompt values verbatim to the line-oriented pyvenv.cfg format while PyEnvCfg._read_values() parses the file with str.splitlines() and accepts the last value for duplicate keys. An attacker who influences --prompt, VIRTUALENV_PROMPT, or configuration input can insert a recognized line boundary and additional keys, including home, causing consumers to use an attacker-selected base interpreter or corrupted environment metadata. The security impact requires prompt input from outside the operator's trust boundary; directly supplied prompt content primarily corrupts the operator's own environment. This issue is fixed in version 21.7.11.

Affected products

Pypi Virtualenv: before 21.7.11; 0.8, 0.8.1, 0.8.2, 0.8.3, 0.8.4, 0.9 (+274) — fixed in 21.7.11
pypa virtualenv: before 21.7.11

How to fix

Upgrade to a fixed version: Pypi Virtualenv 21.7.11. Check the vendor advisory for mitigations.

References

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