CVE-2020-26709
📋 TL;DR
CVE-2020-26709 is an XML External Entity (XXE) vulnerability in py-xml v1.0 that allows attackers to execute arbitrary code by processing a malicious XML file. This affects any application using the vulnerable py-xml library to parse untrusted XML input. Developers and systems processing XML from external sources are at risk.
💻 Affected Systems
- py-xml
📦 What is this software?
Py Xml by Py Xml Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data exfiltration, and lateral movement within the network.
Likely Case
Server-side request forgery (SSRF), file disclosure from the server, or denial of service through resource exhaustion.
If Mitigated
Limited impact if XML parsing is restricted to trusted sources or proper input validation is implemented.
🎯 Exploit Status
Exploitation requires the application to parse attacker-controlled XML. Public proof-of-concept exists in GitHub issues.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v1.0.1 or later
Vendor Advisory: https://github.com/PinaeOS/py-xml/issues/2
Restart Required: No
Instructions:
1. Update py-xml to v1.0.1 or later using pip: pip install --upgrade py-xml
2. Verify the update with: pip show py-xml
3. Restart any applications using the library.
🔧 Temporary Workarounds
Disable external entity processing
allConfigure XML parser to disable external entity resolution
parser = xml.etree.ElementTree.XMLParser(target=TreeBuilder(), resolve_entities=False)
Input validation and sanitization
allValidate and sanitize XML input before processing
🧯 If You Can't Patch
- Implement strict input validation to reject XML containing DOCTYPE declarations or external entity references
- Use network segmentation to isolate systems processing XML from untrusted sources
🔍 How to Verify
Check if Vulnerable:
Check py-xml version: pip show py-xml | grep VersionCheck Version:
pip show py-xml | grep VersionVerify Fix Applied:
Confirm version is 1.0.1 or higher: pip show py-xml | grep Version📡 Detection & Monitoring
Log Indicators:
- Unusual XML parsing errors
- Unexpected file read operations
- Outbound connections to unexpected IPs from XML parsing processes
Network Indicators:
- HTTP requests to internal resources from XML parsing services
- Unexpected DNS queries for internal hostnames
SIEM Query:
source="application.logs" AND ("DOCTYPE" OR "ENTITY" OR "SYSTEM") AND process="xml_parser"