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Response snapshot Oct 27, 2026, 05:12 UTC

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VulnerabilityCVE-2026-113713

virtualenv: Temporary app-data can leave dangling seed package links

The app-data seeder can leave an environment linked to temporary package files that virtualenv deletes when creation finishes. The environment-variable and configuration-file forms of `symlink_app_data` can enable this state even though the command-line flag is disabled for temporary app-data.

Published Updated

At a glance

Exploited
Not known
Severity
4.4 Medium (CVSS 4.0)
Chance of exploitation
0.1% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: virtualenv: 21.14.10. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-4f8h-vr72-p32c (opens a new tab)

What happened

## Summary

The app-data seeder can leave an environment linked to temporary package files that virtualenv deletes when creation finishes. The environment-variable and configuration-file forms of `symlink_app_data` can enable this state even though the command-line flag is disabled for temporary app-data. The resulting environment depends on a cache pathname that its owner no longer controls.

Anthropic's OSS Scanner reported this as `ANT-2026-ZOE2GEPC` in `virtualenv-20261015-005`, received on 15 October 2026. This draft records source review and functional remediation checks. The reporter's cross-account code-execution claim has not been independently reproduced.

## Affected area

Continue reading

Integrity of app-data references after temporary cache cleanup.

## Attacker-controlled input

Symlink seeding must be enabled through `VIRTUALENV_SYMLINK_APP_DATA` or `symlink_app_data` in the configuration file, and app-data setup must fall back to a temporary directory. A missing or unwritable configured cache can cause that fallback. Ordinary copy seeding does not leave these references.

The security concern requires a shared temporary-directory parent where another account can acquire the deleted cache pathname, followed by use of the affected environment. That account need not already be able to modify the environment or the private cache while it exists. This differs from the security policy's excluded case of an account that already controls live app-data contents.

On a platform with a temporary-directory parent private to the environment owner, that cross-account condition is absent. Windows functional checks do not establish cross-account exposure under Windows defaults.

## Affected code

The relevant 21.14.8 source is in [symlink seeder](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/seed/embed/via_app_data/via_app_data.py), [temporary cache cleanup](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/app_data/via_tempdir.py).

## Mechanism

When app-data setup falls back to a temporary directory, the command-line `--symlink-app-data` action is disabled. A value supplied by `VIRTUALENV_SYMLINK_APP_DATA` or `virtualenv.ini` can still become the parser default, and the seeder constructor accepts that value without rechecking the cache lifetime. It links `site-packages/pip` into the temporary cache.

Session cleanup deletes that cache, leaving a dangling link whose pathname can later be claimed by another account on a shared temporary filesystem.

## Reproduction and evidence

The scanner ran its reproduction as two unprivileged users, with root used only to switch identities. The environment owner had an unwritable home, so app-data fell back to `/tmp`. The control used the command-line flag and received a real pip directory. With `VIRTUALENV_SYMLINK_APP_DATA=1`, the new environment instead contained a `pip` link into a deleted `/tmp/tmpXXXXXXXX` directory.

A second uid recreated the target path and placed a fake `pip/__init__.py` there. When the owner ran `venv/bin/pip --version`, that module created a marker inside the owner's environment and printed `this is not pip`.

The cross-account path requires a shared temporary parent, a second account able to claim the deleted name, and later use of the environment. A private temporary parent removes that route. The report traces the incomplete temporary-cache guard to #1661, first released in 20.0.6. [Public fix PR #3437](https://github.

com/pypa/virtualenv/pull/3437) copies packages whenever app-data is temporary, whatever supplied the symlink option. The implementation review checked the remediation; it did not rerun the cross-account reproduction.

## Attack sequence

```mermaid sequenceDiagram participant U as Environment owner participant V as virtualenv seeder participant T as Temporary app-data in /tmp participant E as site-packages/pip link participant A as Other local account U->>V: VIRTUALENV_SYMLINK_APP_DATA=1 with unwritable home V->>T: create transient cache V->>E: link pip to cache path V->>T: delete cache at session exit A->>T: reclaim old name and plant fake pip U->>E: run bin/pip --version E->>T: import fake pip through stale link T-->>U: attacker's code runs as owner ```

## Reproducer files

The following files are from the scanner report for `ANT-2026-ZOE2GEPC`. 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 os import pwd import shutil import subprocess from pathlib import Path

owner = pwd.getpwnam("nobody") # home is /nonexistent: app-data cannot be created, so virtualenv uses a temporary one other_user_uid = 4242 project = Path("/srv/project") other_user_files = Path("/var/tmp/other-user")

# set up: a project folder only the owner can write, and the other user's two files in a folder of their own shutil.rmtree(project, ignore_errors=True) shutil.rmtree(other_user_files, ignore_errors=True) project.mkdir(mode=0o755) os.chown(project, owner.pw_uid, owner.pw_gid) shutil.copytree("/tmp/repro.d", other_user_files) subprocess.run(["chown", "-R", f"{other_user_uid}:{other_user_uid}", other_user_files], check=True)

as_owner = {"user": owner.pw_uid, "group": owner.pw_gid, "extra_groups": [], "cwd": project} as_other_user = {"user": other_user_uid, "group": other_user_uid, "extra_groups": [], "cwd": "/"} owner_env = {"HOME": owner.pw_dir, "PATH": os.environ["PATH"]} virtualenv = ["virtualenv", "--quiet", "--no-periodic-update"]

# control: --symlink-app-data on the command line is dropped while app-data is temporary, so pip is copied subprocess.run([*virtualenv, "--symlink-app-data"

Affected package ranges reported by GitHub: virtualenv: >= 21.14.8, < 21.14.10

Scores and how they were measured

CVSS base severity

4.4

Version 4.0As of

CVSS:4.0/AV:L/AC:H/AT:P/PR:L/UI:P/VC:L/VI:H/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

0.1%

Scored Percentile 3.2%

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-4f8h-vr72-p32c (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-4f8h-vr72-p32c, 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-2026-113713, 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: Temporary app-data can leave dangling seed package links (CVE-2026-113713). https://kevwire.com/record/CVE-2026-113713

MLA

"virtualenv: Temporary app-data can leave dangling seed package links (CVE-2026-113713)." KEVWire, 23 Oct. 2026, kevwire.com/record/CVE-2026-113713.

Chicago

KEVWire. "virtualenv: Temporary app-data can leave dangling seed package links (CVE-2026-113713)." Last modified October 23, 2026. https://kevwire.com/record/CVE-2026-113713.

Evidence summary (plain text)

virtualenv: Temporary app-data can leave dangling seed package links (Oct 23, 2026).
The app-data seeder can leave an environment linked to temporary package files that virtualenv deletes when creation
finishes. The environment-variable and configuration-file forms of `symlink_app_data` can enable this state even though
the command-line flag is disabled for temporary app-data. The resulting environment depends on a cache pathname that its
owner no longer controls.

Anthropic's OSS Scanner reported this as `ANT-2026-ZOE2GEPC` in `virtualenv-20261015-005`, received on 15 October 2026.
This draft records source review and functional remediation checks. The reporter's cross-account code-execution claim
has not been independently reproduced.
CVSS 4.4 (version 4.0; evidence as of Oct 23, 2026; https://github.com/advisories/GHSA-4f8h-vr72-p32c).
EPSS 0.1% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-113713&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-4f8h-vr72-p32c: https://github.com/advisories/GHSA-4f8h-vr72-p32c
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-2026-113713&date=2026-10-26
Record ID: CVE-2026-113713.
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 27, 2026, 01:40 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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