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Response snapshot Oct 27, 2026, 00:06 UTC

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VulnerabilityCVE-2026-113717

virtualenv: Pip seeding with download omits wheel digest verification

The pip seeder acquires bundled wheels with download=False and lets pip access the index when --download is selected. Index candidates on that path do not pass through virtualenv's wheel digest verification.

Published Updated

At a glance

Exploited
Not known
Severity
2.3 Low (CVSS 4.0)
Chance of exploitation
0.3% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: virtualenv: 21.14.9. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-cx28-75q4-x26q (opens a new tab)

What happened

## Summary

The pip seeder acquires bundled wheels with download=False and lets pip access the index when --download is selected. Index candidates on that path do not pass through virtualenv's wheel digest verification.

Anthropic's OSS Scanner reported this as `ANT-2026-74ALJBUF` in `virtualenv-20261015-005`, received on 15 October 2026.

## Affected area

Continue reading

Wheel selection by the pip seeder when downloads are enabled.

## Attacker-controlled input

The pip seeder and download option must be selected. The finding concerns the default-index digest-verification policy. Explicit custom-index settings already opt out of comparison against PyPI metadata; this patch retains that policy.

## Affected code

The relevant 21.14.8 source is in [pip seeder](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/seed/embed/pip_invoke.py).

## Mechanism

With `--seeder pip --download`, `PipInvoke.get_pip_install_cmd()` first calls `get_wheel(download=False)`, so virtualenv's `download_wheel()` and `verify_wheel_digest()` are skipped. It then lets `pip install` consult the configured index. An index wheel with the same package and version as the bundled wheel can be selected without virtualenv comparing its SHA-256 with PyPI metadata. The default app-data seeder takes the verification path for the same option.

## Reproduction and evidence

The scanner built a local index named in `pip.conf` that served a modified copy of the bundled pip wheel under the same filename. In the control run, `virtualenv --download env-default` rejected the wheel with a digest mismatch. In the second run, adding `--seeder pip` produced an environment whose installed `pip/__init__.py` matched the index wheel; `env-pip/bin/pip --version` ran the added line. The reproducer checked the installed bytes and marker before reporting `BUG`.

Both `--seeder pip` and `--download` are needed. The report used a non-PyPI index from `pip.conf` and left `PIP_INDEX_URL`, `PIP_EXTRA_INDEX_URL`, and `PIP_INDEX` unset, so virtualenv's default-seeder PyPI comparison remained active. This does not establish index control in the default PyPI setup.

The unchecked pip-seeder download path is older, while the comparison with the default seeder arose when digest verification was added in 21.7.12. [PR #3430](https://github.com/pypa/virtualenv/pull/3430) acquires and verifies selected wheels before invoking pip with index lookup disabled.

## Attack sequence

```mermaid sequenceDiagram participant I as Index in pip.

conf participant V as virtualenv PipInvoke participant P as pip install participant E as Seeded environment I->>V: serve modified pip wheel V->>V: get_wheel(download=False) V->>P: install with --download permitting index lookup P->>I: select same-version index wheel I->>E: modified pip installed without virtualenv digest check E->>E: later pip invocation runs added code Note over V,E: Default app-data seeder rejects the same digest ```

## Reproducer files

The following files are from the scanner report for `ANT-2026-74ALJBUF`. They were tested against commit `a857a7823c73` in the scanner image. The `repro` entrypoint expects companion files under `/tmp/repro.d`; cases that change user IDs need a disposable root-capable container. The last output line is `BUG` when the reported behavior occurs. These files are included as evidence and were not rerun for this advisory update.

**`repro`**

```text #!/usr/bin/env python3 import glob import hashlib import json import os import shutil import subprocess import sys import zipfile

from virtualenv.seed.wheels.embed import get_embed_wheel

companions = "/tmp/repro.d" work = "/tmp/repro-pip-seeder-download" shutil.rmtree(work, ignore_errors=True) os.makedirs(work)

# set up: the pip wheel virtualenv bundles, and PyPI's record of its sha256 (served by virtualenv_offline.py: no network) bundled = get_embed_wheel("pip", f"{sys.version_info.major}.{sys.version_info.minor}") pypi_sha256 = hashlib.sha256(open(bundled.path, "rb").read()).hexdigest() pypi_release = {"filename": bundled.name, "digests": {"sha256": pypi_sha256}} os.makedirs(f"{work}/pypi.

org/pypi/pip") with open(f"{work}/pypi.org/pypi/pip/json", "w") as pypi_json: json.dump({"releases": {bundled.version: [pypi_release]}}, pypi_json)

# attacker: the mirror serves other bytes under the bundled wheel's own file name marker = f"{work}/MIRROR_CODE_RAN" subprocess.run([sys.executable, f"{companions}/make_mirror.py", str(bundled.path), f"{work}/mirror", marker], check=True) mirror_wheel = f"{work}/mirror/pip/{bundled.name}" mirror_sha256 = hashlib.sha256(open(mirror_wheel, "rb").read()).hexdigest() print(f"{bundled.

name}: PyPI publishes sha256 {pypi_sha256}") print(f"{bundled.name}: the mirror serves sha256 {mirror_sha256}")

# user: pip.conf names the mirror; PIP_INDEX_URL, PIP_EXTRA_INDEX_URL and PIP_INDEX (which turn the check off) are unset with open(f"{work}/pip.conf", "w") as pip_conf: pip_conf.write(f"[global]\nindex-url = file://{work}/mirror\n") # file:// stands in for the mirror's http URL os.makedirs(f"{work}/home-default") os.

makedirs(f"{work}/home-pip") # one HOME per run, so neither sees the other's app-data or pip cache virtualenv = [sys.executable, f"{companions}/virtualenv_offline.py", f"{work}/pypi.org", "--no-periodic-update"]

# control: the default seeder with --download fetches the mirror's wheel and refuses it default_seeder = subprocess.run( [*virtualenv, "--download", f"{work}/env-default"], env={**os.environ, "HOME": f"{work}/home-default", "PIP_CONFIG_FILE": f"{work}/pip.conf"}, capture_output=True, text=True, ) refusal = [line for line in default_seeder.stdout.splitlines() if line.

startswith("RuntimeError: ")] print(f"\nCONTROL virtualenv --download env-default: exit {default_seeder.returncode}") print("\n".join(refusal))

# trigger: the same command plus --seeder pip pip_seeder = subprocess.run( [*virtualenv, "--download", "--seeder", "pip", f"{work}/env-pip"],

Affected package ranges reported by GitHub: virtualenv: < 21.14.9

Scores and how they were measured

CVSS base severity

2.3

Version 4.0As of

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.3%

Scored Percentile 21.7%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-cx28-75q4-x26q (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-cx28-75q4-x26q, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-113717, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 23). virtualenv: Pip seeding with download omits wheel digest verification (CVE-2026-113717). https://kevwire.com/record/CVE-2026-113717

MLA

"virtualenv: Pip seeding with download omits wheel digest verification (CVE-2026-113717)." KEVWire, 23 Oct. 2026, kevwire.com/record/CVE-2026-113717.

Chicago

KEVWire. "virtualenv: Pip seeding with download omits wheel digest verification (CVE-2026-113717)." Last modified October 23, 2026. https://kevwire.com/record/CVE-2026-113717.

Evidence summary (plain text)

virtualenv: Pip seeding with download omits wheel digest verification (Oct 23, 2026).
The pip seeder acquires bundled wheels with download=False and lets pip access the index when --download is selected.
Index candidates on that path do not pass through virtualenv's wheel digest verification.

Anthropic's OSS Scanner reported this as `ANT-2026-74ALJBUF` in `virtualenv-20261015-005`, received on 15 October 2026.
CVSS 2.3 (version 4.0; evidence as of Oct 23, 2026; https://github.com/advisories/GHSA-cx28-75q4-x26q).
EPSS 0.3% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-113717&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-cx28-75q4-x26q: https://github.com/advisories/GHSA-cx28-75q4-x26q
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-113717&date=2026-10-26
Record ID: CVE-2026-113717.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 19:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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