Summary
A path traversal vulnerability exists in GuardDog's safeextract() function that allows malicious PyPI packages to write arbitrary files outside the intended extraction directory, leading to Arbitrary File Overwrite and Remote Code Execution on systems running GuardDog.
CWE: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)
Details
Vulnerable Code
File: guarddog/utils/archives.py
python elif zipfile.iszipfile(sourcearchive): with zipfile.ZipFile(sourcearchive, "r") as zip: for file in zip.namelist(): # Note: zip.extract cleans up any malicious file name # such as directory traversal attempts This is not the # case of zipfile.extractall zip.extract(file, path=os.path.join(targetdirectory, file)) # ❌ VULNERABLE
Root Cause
The comment about zip.extract() fooled me at first :) then I noticed the os.path.join() call. The vulnerability stems from incorrect usage of Python's zipfile.ZipFile.extract() API:
- The path parameter should be the target directory, not a full file path - extract() automatically appends the member name to the path - By passing os.path.join(targetdirectory, file), GuardDog causes the filename to be appended twice - This breaks zipfile's built-in path traversal sanitization
Attack Vector
1. Attacker creates malicious wheel with path traversal filenames 2. Uploads to PyPI or distributes directly 3. Package scan: guarddog pypi scan malicious-pkg 4. GuardDog downloads and extracts the package 5. Malicious files written to arbitrary locations 6. Code execution could be achieved
Impact
Impact depends on how GuardDog is running and under which environment.
Critical Scenarios
1. Immediate Code Execution - Write to ~/.bashrc → executes on next shell - Write to ~/.profile → executes on login
2. Persistent Backdoors - Write to ~/.ssh/authorizedkeys → SSH access - Write to /etc/cron.d/malicious → scheduled execution (if root) - Write to systemd user services → persistent execution
and more...
Credits
Reported by: Charbel (dwbruijn)
Summary
GuardDog's safeextract() function does not validate decompressed file sizes when extracting ZIP archives (wheels, eggs), allowing attackers to cause denial of service through zip bombs. A malicious package can consume gigabytes of disk space from a few megabytes of compressed data.
Vulnerability Details
Affected Component: guarddog/utils/archives.py - safeextract() function Vulnerability Type: CWE-409 - Improper Handling of Highly Compressed Data (Zip Bomb) Severity: HIGH (CVSS ~8) Attack Vector: Network (malicious package uploaded to PyPI/npm) or local
Root Cause
The safeextract() function handles TAR files securely using the tarsafe library, but ZIP file extraction has no size validation: python elif zipfile.iszipfile(sourcearchive): with zipfile.ZipFile(sourcearchive, "r") as zip: for file in zip.namelist(): zip.extract(file, path=os.path.join(targetdirectory, file))
Missing protections: - ❌ No decompressed size limit - ❌ No compression ratio validation - ❌ No file count limits - ❌ No total extracted size validation
Impact
Denial of Service Scenarios
1. CI/CD Pipeline Disruption - Attacker publishes malicious package to PyPI - Developer adds package to requirements.txt - CI/CD runs GuardDog scan - Disk fills (GitHub Actions: standard 14GB limit) - All deployments blocked
2. Resource Exhaustion - Local development environments - Security scanning infrastructure - Automated scanning systems - Docker containers with limited disk
3. Supply Chain Attack Amplification - Single malicious package blocks security scanning - Prevents detection of other malicious packages - Forces manual intervention - Increases security team workload
Recommended Fix
Add size validation for ZIP files similar to what tarsafe provides for TAR files
Configuration Options
Make limits configurable via environment variables or config file
Additional Improvements
1. Add warning logs when archives approach limits 2. Provide clear error messages for users 3. Document limits in user-facing documentation 4. Add tests for zip bomb detection 5. Consider using a safe ZIP library (similar to tarsafe)
Credit
Reported by: Charbel (dwbruijn)