Backport venv activation scripts escaping improvements from virtualenv

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Évaluation

Difficulté
4/5
Temps estimé
3-5 jours
Accessibilité débutants
42/100
Type d'issue
Bug
Clarté
Plutôt claire
Activité
Active
Stack technique
bash, fish, python, zsh
Domaine
backend, security

Piste de recherche

Start by comparing CPython's venv activation script generation and pyvenv.cfg writing with the seven linked virtualenv commits. Use the reproduction script on Linux with Python 3.14, 3.15, and 3.16 to identify which cases occur, then inspect the corresponding venv implementation and tests. Done means the applicable escaping and file handling issues are fixed and regression tests cover the reported cases.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Description

stdlib topic-venv type-bug
Bug report

In Fedora, we have recently triaged some CVE that were publicly displosed for pypa/virtualenv. I decided to check if anything is also reproducible via plain venv and it is.

CVE-2026-113723, CVE-2026-113725, CVE-2026-113726, CVE-2026-113732, CVE-2026-113715, CVE-2026-113716, CVE-2026-113721

Neither is considered a security vulnerability in CPython:

Vulnerabilities must not depend on malicious control of Python’s launch conditions, including (but not limited to) command line arguments, environment variables, or modifications to files on the target system. We assume that, at the time Python is executed, the environment is as intended by the legitimate user, and any malicious variation from this cannot be mitigated by Python itself.

However, those issues are still nice to fix.

To reproduce:

#!/bin/bash
set -u
for PY in python3.14 python3.15 python3.16; do
  echo "################## $PY ##################"
  WORK=$(mktemp -d)
  cd "$WORK"

  echo "=== 1. bash/zsh PS1 redraw injection ==="
  echo "    cf. virtualenv CVE-2026-113723, CVE-2026-113725, CVE-2026-113726"
  "$PY" -m venv --without-pip --prompt "x\$(touch $WORK/PWNED_BASH)y" "$WORK/venv1" >/dev/null 2>&1
  bash -c "source $WORK/venv1/bin/activate; echo \"\${PS1@P}\"" >/dev/null 2>&1
  test -e "$WORK/PWNED_BASH" && echo "BASH: VULNERABLE" || echo "BASH: not reproduced"

  "$PY" -m venv --without-pip --prompt "x\$(touch $WORK/PWNED_ZSH)y" "$WORK/venv1z" >/dev/null 2>&1
  zsh -c "setopt PROMPT_SUBST; source $WORK/venv1z/bin/activate; print -P \"\$PS1\"" >/dev/null 2>&1
  test -e "$WORK/PWNED_ZSH" && echo "ZSH: VULNERABLE" || echo "ZSH: not reproduced"

  echo "=== 2. fish quote-escaping gap ==="
  echo "    cf. virtualenv CVE-2026-113732"
  mkdir -p "$WORK/workdir2"
  "$PY" -m venv --without-pip --prompt "x\\'\$(touch PWNED)'\\'" "$WORK/venv2" >/dev/null 2>&1
  (cd "$WORK/workdir2" && fish --no-config -c "source $WORK/venv2/bin/activate.fish" >/dev/null 2>&1)
  test -e "$WORK/workdir2/PWNED" && echo "FISH: VULNERABLE" || echo "FISH: not reproduced"

  echo "=== 3. pyvenv.cfg injection via command= ==="
  echo "    cf. virtualenv CVE-2026-113715"
  "$PY" -m venv --without-pip --prompt $'legit\ninclude-system-site-packages = true\n#' "$WORK/venv3" >/dev/null 2>&1
  RESULT=$("$WORK/venv3/bin/$PY" -c "import site; print(site.ENABLE_USER_SITE)" 2>&1)
  echo "ENABLE_USER_SITE=$RESULT"

  echo "=== 4. site-packages redirected via symlinked intermediate dir ==="
  echo "    cf. virtualenv CVE-2026-113716"
  mkdir -p "$WORK/envdir4" "$WORK/outside4"
  ln -s "$WORK/outside4" "$WORK/envdir4/lib"
  "$PY" -m venv --without-pip "$WORK/envdir4" >/dev/null 2>&1
  test -d "$WORK/outside4/$PY/site-packages" && echo "SYMLINK-DIR: VULNERABLE" || echo "SYMLINK-DIR: not reproduced"

  echo "=== 5. file overwrite through pre-existing symlink ==="
  echo "    cf. virtualenv CVE-2026-113721"
  mkdir -p "$WORK/envdir5/bin"
  echo SENSITIVE > "$WORK/outside5"
  ln -s "$WORK/outside5" "$WORK/envdir5/bin/activate"
  "$PY" -m venv --without-pip "$WORK/envdir5" >/dev/null 2>&1
  grep -q "virtualenv\|venv" "$WORK/outside5" 2>/dev/null && echo "SYMLINK-FILE: VULNERABLE" || echo "SYMLINK-FILE: not reproduced"

  rm -rf "$WORK"
  echo
done

virtualenv fixes:

CPython versions tested on:

3.16, 3.15, 3.14

Operating systems tested on:

Linux

Linked PRs
  • gh-160943
  • gh-160971
  • gh-160972
  • gh-160973
Langage dominant
Python
Étoiles
77.8k
Forks
37.7k
Merge moyen
17 h 24 min
PR mergées (30 j)
716

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