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BREW-charm-tools-CVE-2026-113716 — virtualenv: Builtin creation follows linked environment directories

Affected: Homebrew: charm-tools

## Summary

The builtin creator accepts existing directory symlinks through ensure_dir() and writes environment files through those directories. This permits writes outside the requested destination.

Anthropic's OSS Scanner reported this as `ANT-2026-MUFJEG11` in `virtualenv-20261015-005`, received on 15 October 2026.

## Affected area

Directory preparation before environment files are created.

## Attacker-controlled input

Another account must be able to prepare linked entries below the chosen destination before creation. The invoking user must have access to the linked destination. This does not require write access to the target itself under the other account.

## Affected code

The relevant 21.14.8 source is in [builtin creator](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/create/via_global_ref/builtin/via_global_self_do.py), [ensure_dir()](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/util/path/_sync.py).

## Mechanism

The builtin creator calls `ensure_dir()` for `bin`, `lib`, and package directories. `ensure_dir()` accepts an existing symlink to a directory because `exists()` follows it. Interpreter creation, seed installation, and activation-script generation then write through that parent link. A final-file check cannot prevent a write through a linked parent. `--clear` removes the planted tree first; ordinary creation over a prepared destination reaches it.

## R…

fkie_cve-2026-113716

virtualenv is a tool for creating isolated virtual python environments. Prior to 21.14.9, the builtin creator calls ensure_dir() for executable, library, and package directories, and ensure_dir() accepts an existing symlink to a directory because exists() follows it. Interpreter creation, seed installation, and activation generation then write through the linked parent outside the requested destination when another local account prepared the tree and the invoking user can access the target. The --clear option removes the planted tree first, while ordinary creation reaches it; arbitrary attacker-selected output bytes are not established. This issue is fixed in version 21.14.9.

GHSA-cw65-gx24-rc82 — virtualenv: Builtin creation follows linked environment directories

Affected: PyPI: virtualenv