CVE-2018-20027
📋 TL;DR
CVE-2018-20027 is a critical code injection vulnerability in Pylearn2's yaml_parse.load method that allows remote attackers to execute arbitrary code by providing malicious YAML input. This affects any application using Pylearn2 to parse untrusted YAML data. The vulnerability is particularly dangerous because it can be exploited without authentication.
💻 Affected Systems
- Pylearn2
📦 What is this software?
Pylearn2 by Lisa Lab
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with remote code execution, allowing attackers to install malware, exfiltrate data, or pivot to other systems.
Likely Case
Remote code execution leading to data theft, system manipulation, or deployment of ransomware/cryptominers.
If Mitigated
Limited impact if proper input validation and sandboxing prevent code execution, though denial of service may still occur.
🎯 Exploit Status
Simple proof-of-concept exploits exist demonstrating remote code execution. The vulnerability is easy to exploit with basic Python knowledge.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in the repository, but Pylearn2 is no longer actively maintained
Vendor Advisory: https://github.com/lisa-lab/pylearn2/issues/1593
Restart Required: No
Instructions:
1. Update to the latest Pylearn2 version from GitHub. 2. Replace yaml_parse.load() with yaml.safe_load() in all code. 3. Test applications thoroughly after changes.
🔧 Temporary Workarounds
Replace yaml_parse.load with yaml.safe_load
allReplace vulnerable yaml_parse.load() calls with PyYAML's safe_load() which prevents code execution
Replace: yaml_parse.load(yaml_string)
With: yaml.safe_load(yaml_string)
Input validation and sanitization
allImplement strict input validation to reject suspicious YAML content before processing
🧯 If You Can't Patch
- Network segmentation to isolate vulnerable systems from critical assets
- Implement strict access controls and monitor for suspicious YAML processing activity
🔍 How to Verify
Check if Vulnerable:
Search codebase for 'yaml_parse.load' calls and check if they process untrusted inputCheck Version:
Check Python imports and usage patterns rather than version numbers since Pylearn2 is no longer versionedVerify Fix Applied:
Verify all yaml_parse.load() calls have been replaced with yaml.safe_load() and test with malicious YAML payloads📡 Detection & Monitoring
Log Indicators:
- Unusual process execution from Python applications
- Errors in YAML parsing logs
- Suspicious network connections from Python processes
Network Indicators:
- Unexpected outbound connections from applications processing YAML
- Traffic patterns suggesting data exfiltration
SIEM Query:
Process execution where parent process is python AND command contains suspicious patterns like 'os.system' or 'subprocess'