Summary
Unsafe extracting using shutil.unpackarchive() from a remotely retrieved tarball may lead to writing the extracted file to an unintended destination.
Details
Extracting files using shutil.unpackarchive() from a potentially malicious tarball without validating that the destination file path is within the intended destination directory can cause files outside the destination directory to be overwritten.
The vulnerable code snippet is between L153..158.
python response = requests.get(url, stream=True)
with open(zippath, "wb") as f: f.write(response.raw.read())
shutil.unpackarchive(zippath, unzippedpath) It seems that a remotely retrieved tarball which could be with the extension .tar.gz happens to be unpacked using shutil.unpackarchive() with no destination verification/limitation of the extracted files.
PoC
The PoC provided showcases the risk of extracting the non-harmless text file sim4n6.txt to a parent location rather than the current folder.
bash tar --list -f archive.tar tar: Removing leading ../../../' from member names ../../../sim4n6.txt
python3 Python 3.10.6 (main, Nov 2 2022, 18:53:38) [GCC 11.3.0] on linux Type "help", "copyright", "credits" or "license" for more information. >> import shutil >> shutil.unpackarchive("archive.tar") >> exit()
file ../../../sim4n6.txt ../../../sim4n6.txt: ASCII text
A Potential Attack Scenario
- An attacker may craft a malicious tarball with a filename path, such as ../../../../../../../../etc/passwd, and then serve the archive remotely, thus, providing a possibility to overwrite the system files.
Mitigation
Potential mitigation could be to: - Use a safer module, like zipfile. - Validate the location of the extracted files and discard those with malicious paths such as a relative path .. or absolute ones.
Impact
Running GuardDog against a specially-crafted package can allow an attacker to write an arbitrary file on the machine where GuardDog is executed.
This is due to a path traversal vulnerability when extracting the .tar.gz file of the package being scanned, which exists by design in the tarfile.TarFile.extractall function. See also https://docs.python.org/3/library/tarfile.html#tarfile.TarFile.extractall
Remediation
Upgrade to GuardDog v0.1.5 or more recent.
References
https://semgrep.dev/r?q=trailofbits.python.tarfile-extractall-traversal.tarfile-extractall-traversal https://www.trellix.com/en-us/about/newsroom/stories/research/tarfile-exploiting-the-world.html https://docs.python.org/3/library/tarfile.html#tarfile.TarFile.extractall