CVE-2021-20874
📋 TL;DR
This vulnerability allows remote unauthenticated attackers to access arbitrary files on GroupSession servers, potentially exposing sensitive information. It affects GroupSession Free edition, GroupSession byCloud, and GroupSession ZION versions 5.1.1 and earlier. Attackers can exploit this without any authentication.
💻 Affected Systems
- GroupSession Free edition
- GroupSession byCloud
- GroupSession ZION
📦 What is this software?
Groupsession by Groupsession
Groupsession by Groupsession
Groupsession by Groupsession
⚠️ Risk & Real-World Impact
Worst Case
Complete server compromise through access to configuration files, credentials, and sensitive data, potentially leading to data breach and further system exploitation.
Likely Case
Unauthorized access to sensitive files containing configuration data, user information, or other confidential information stored on the server.
If Mitigated
Limited impact with proper network segmentation and access controls preventing external exploitation, though internal threats may still exist.
🎯 Exploit Status
Unspecified vectors but unauthenticated access suggests relatively simple exploitation. No public proof-of-concept identified in references.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 5.1.1
Vendor Advisory: https://groupsession.jp/info/info-news/security20211220
Restart Required: Yes
Instructions:
1. Download latest version from official GroupSession website. 2. Backup current installation. 3. Apply update following vendor instructions. 4. Restart GroupSession service. 5. Verify update completed successfully.
🔧 Temporary Workarounds
Network Access Restriction
linuxRestrict network access to GroupSession service to trusted IP addresses only
iptables -A INPUT -p tcp --dport [GroupSession_port] -s [trusted_network] -j ACCEPT
iptables -A INPUT -p tcp --dport [GroupSession_port] -j DROP
File System Permissions Hardening
linuxTighten file system permissions on sensitive directories to prevent unauthorized access
chmod 750 /path/to/groupsession/data
chmod 640 /path/to/groupsession/config/*
🧯 If You Can't Patch
- Implement strict network segmentation and firewall rules to isolate GroupSession servers from untrusted networks
- Deploy web application firewall (WAF) with file access protection rules and monitor for directory traversal attempts
🔍 How to Verify
Check if Vulnerable:
Check GroupSession version in admin panel or configuration files. If version is 5.1.1 or earlier, system is vulnerable.Check Version:
Check web interface admin panel or examine version.txt in installation directoryVerify Fix Applied:
Verify version is updated to 5.2.0 or later in admin panel and test file access attempts return proper access denied errors.📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns
- Multiple failed file access attempts
- Access to sensitive file paths from unauthenticated users
Network Indicators:
- HTTP requests attempting directory traversal patterns
- Requests for sensitive file paths without authentication
SIEM Query:
source="groupsession" AND (url="*../*" OR url="*/etc/*" OR url="*/config/*") AND user="-"