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PYSEC-2026-4011
virtualenvdownload_wheel() runs pip download and hands the result straight to the
seeder, with nothing checking the bytes it gets back. The embedded pip and
setuptools wheels carry a BUNDLE_SHA256 that virtualenv checks on every load,
but a wheel fetched over the network for the periodic-update feature or the
--download flag had no equivalent verification.
A compromised index, a stale mirror, or a MITM'd download (when TLS is intercepted, e.g. via a misconfigured or malicious CA) could substitute a different wheel under the same distribution/version/filename, and virtualenv would cache and seed it into every environment created afterward with no warning.
Fixed in 21.7.12 by computing the downloaded wheel's sha256 and comparing it
against the digest PyPI's public JSON API reports for that exact release,
independent of which index actually served the file. The check is skipped, not
treated as failure, when a custom index (PIP_INDEX_URL,
PIP_EXTRA_INDEX_URL, PIP_INDEX) is configured, since a private index can
legitimately serve a different, intentionally rebuilt wheel.
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Measures severity based on intrinsic characteristics of the vulnerability, independent of environment.
No exploitation activity has been observed at this time. Continue routine monitoring.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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