CVE-2021-26703
📋 TL;DR
CVE-2021-26703 is a critical vulnerability in EPrints 3.4.2 that allows remote attackers to read arbitrary files and potentially execute commands via crafted JSON/XML input to specific CGI endpoints. This affects all EPrints 3.4.2 installations with the vulnerable ajax/phrase functionality exposed. Attackers can exploit this without authentication to compromise the server.
💻 Affected Systems
- EPrints
📦 What is this software?
Eprints by Eprints
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data exfiltration, and lateral movement within the network.
Likely Case
Arbitrary file reading exposing sensitive configuration files, credentials, and database information, potentially leading to further exploitation.
If Mitigated
Limited impact if proper input validation and file access controls are implemented, though information disclosure may still occur.
🎯 Exploit Status
Exploitation is straightforward with publicly available proof-of-concept code. Attackers can craft malicious JSON/XML payloads to trigger the vulnerability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.4.3 and later
Vendor Advisory: https://files.eprints.org/2548/
Restart Required: Yes
Instructions:
1. Backup your EPrints installation and database. 2. Download EPrints 3.4.3 or later from the official repository. 3. Replace the vulnerable files with the patched version. 4. Restart the web server and EPrints services. 5. Verify the fix by testing the vulnerable endpoint.
🔧 Temporary Workarounds
Disable vulnerable CGI endpoint
allTemporarily disable or restrict access to the cgi/ajax/phrase endpoint to prevent exploitation.
# In Apache config: <Location "/cgi/ajax/phrase"> Deny from all </Location>
# In Nginx config: location ~ ^/cgi/ajax/phrase { deny all; }
Input validation filter
allImplement strict input validation for JSON/XML parsing in the ajax/phrase handler.
# Modify the Perl script to validate and sanitize input before processing
🧯 If You Can't Patch
- Implement strict network access controls to limit access to the EPrints server to trusted IPs only.
- Deploy a web application firewall (WAF) with rules to block malicious JSON/XML payloads targeting the vulnerable endpoint.
🔍 How to Verify
Check if Vulnerable:
Test if the /cgi/ajax/phrase endpoint accepts JSON/XML input and returns file contents when crafted payloads are sent. Use curl: curl -X POST -H 'Content-Type: application/json' --data '{"test":"payload"}' http://target/cgi/ajax/phraseCheck Version:
Check the EPrints version in the web interface or via the installation directory: cat /path/to/eprints/version.txtVerify Fix Applied:
After patching, attempt the same test and verify that file reading/command execution no longer occurs. The endpoint should return appropriate error messages or sanitized responses.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /cgi/ajax/phrase with JSON/XML payloads
- Error logs showing file access attempts or command execution failures
- Increased traffic to the ajax endpoint from suspicious IPs
Network Indicators:
- HTTP POST requests with crafted JSON/XML to the vulnerable endpoint
- Outbound connections from the EPrints server to unknown destinations post-exploitation
SIEM Query:
source="web_logs" AND uri="/cgi/ajax/phrase" AND (method="POST" OR method="PUT") AND (content_type="application/json" OR content_type="application/xml")