virtualenv EUVD-2026-105298

Requires virtualenv prior to 21.14.9 invoked with --seeder pip and --download, while pip/virtualenv index environment variables remain unset so the default-index PyPI SHA-256 comparison policy stays active, AND a non-PyPI index is in use that offers a candidate matching the bundled package name and version. The user must actively run the virtualenv seeding operation (UI:P). Explicit custom-index configurations already opt out of the comparison and are outside this issue. Strong limiting factors: the bypass does not defeat TLS and does not give the attacker control of the index response, exploitation is high-complexity with specific attack requirements, and resulting impact is only low integrity - so realistic risk is far below what the network vector alone suggests.

This is a genuinely low-priority issue despite a network attack vector. The vendor CVSS 4.0 base score is only 2.3, and the composite signals explain why: AV:N but AC:H (high complexity) and AT:P (specific attack requirements must be present), with UI:P meaning a user must actively run virtualenv seeding, and only Low vulnerable-system impact (VC:L/VI:L/VA:L). No EPSS score, KEV listing, or public POC is present in the provided data, so exploitation likelihood signals are all absent rather than elevated. The flaw is a narrow integrity-verification gap (CWE-494): the pip seeder's --download path bypassed virtualenv's download_wheel()/verify_wheel_digest() SHA-256 comparison against PyPI metadata. Critically, the description itself states this condition does NOT defeat TLS or grant control of the index response, so an attacker cannot trivially inject a malicious wheel - they would need an index that already legitimately serves a candidate matching the bundled name and version. PR:N (unauthenticated per the 4.0 vector) is technically accurate but misleading in isolation: real-world abuse depends on an attacker already being positioned as a non-PyPI index source. Treat this as a defense-in-depth hardening fix, not an actively-weaponizable vulnerability.

An organization bootstraps environments with virtualenv (< 21.14.9) using --seeder pip --download while index environment variables are left unset, so the default-index PyPI digest comparison policy is active but a non-PyPI index is in use. pip is allowed to consult that index and select a candidate matching the bundled package name and version without virtualenv comparing its SHA-256 against PyPI metadata, so an unverified wheel can be seeded into the new environment. No public exploit identified at time of analysis, and the condition does not by itself defeat TLS or let the attacker forge the index response.