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BIT-virtualenv-2026-113718 — virtualenv: Xonsh activation literals depend on the script decoding codec

2026-10-31T23:20:27.035405+00:00

Affected: Bitnami: virtualenv

virtualenv is a tool for creating isolated virtual python environments. Prior to 21.14.9, POSIX xonsh activation quote() uses repr() to write printable non-ASCII prompt or destination data into UTF-8 activate.xsh, while xonsh can read that script using $XONSH_ENCODING. Under a legacy multibyte codec such as GBK or Big5, a UTF-8 trail byte can consume the backslash before an adjacent quote, allowing the literal to close and attacker-influenced statements to execute when the user sources the generated script. This issue is fixed in version 21.14.9.

CVE-2026-113718 — virtualenv: Xonsh activation literals depend on the script decoding codec

2026-10-31T23:20:27.035477+00:00

Affected: pypa virtualenv

GHSA-394h-qwmc-48pf — virtualenv: Xonsh activation literals depend on the script decoding codec

2026-10-31T23:20:27.035513+00:00

Affected: PyPI: virtualenv

## 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.

## 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 strin…