CVE-2021-27730
📋 TL;DR
CVE-2021-27730 is an argument injection vulnerability in Accellion FTA that allows attackers to execute arbitrary commands via crafted POST requests to admin endpoints. This affects all Accellion FTA versions up to 9_12_432. Organizations using vulnerable Accellion FTA installations are at risk of complete system compromise.
💻 Affected Systems
- Accellion File Transfer Appliance (FTA)
📦 What is this software?
Fta by Accellion
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise leading to data exfiltration, ransomware deployment, lateral movement, and persistent backdoor installation
Likely Case
Remote code execution allowing attackers to steal sensitive data, deploy malware, or disrupt file transfer operations
If Mitigated
Limited impact through network segmentation and strict access controls, potentially preventing exploitation
🎯 Exploit Status
Exploitation requires access to admin endpoints but is straightforward once access is obtained. Multiple threat actors have weaponized this vulnerability in real attacks.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FTA_9_12_444 and later
Vendor Advisory: https://github.com/accellion/CVEs/blob/main/CVE-2021-27730.txt
Restart Required: Yes
Instructions:
1. Download FTA_9_12_444 or later from Accellion support portal. 2. Backup current configuration. 3. Apply the patch following Accellion's upgrade documentation. 4. Restart the FTA service. 5. Verify the patch is applied successfully.
🔧 Temporary Workarounds
Network Access Restriction
linuxRestrict access to FTA admin endpoints using firewall rules or network segmentation
iptables -A INPUT -p tcp --dport [FTA_ADMIN_PORT] -s [TRUSTED_IPS] -j ACCEPT
iptables -A INPUT -p tcp --dport [FTA_ADMIN_PORT] -j DROP
Admin Interface IP Whitelisting
allConfigure FTA to only allow admin access from specific IP addresses
Configure via FTA web interface: Admin > Security > Access Control
🧯 If You Can't Patch
- Isolate the FTA appliance in a dedicated network segment with strict firewall rules
- Implement multi-factor authentication for all admin accounts and monitor for suspicious activity
🔍 How to Verify
Check if Vulnerable:
Check FTA version via web interface (Admin > System > About) or SSH: cat /usr/local/accellion/fta/version.txtCheck Version:
cat /usr/local/accellion/fta/version.txtVerify Fix Applied:
Verify version is 9_12_444 or higher and test admin endpoint functionality📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to admin endpoints
- Suspicious command execution in system logs
- Multiple failed authentication attempts followed by successful admin access
Network Indicators:
- Unusual outbound connections from FTA appliance
- Traffic patterns indicating data exfiltration
- Unexpected process execution on standard ports
SIEM Query:
source="fta_logs" AND (uri_path="/admin/*" AND http_method="POST" AND (user_agent="*curl*" OR user_agent="*wget*" OR size_bytes>1000000))