Accellion FTA Remote OS Command Execution Vulnerability (CVE-2021-27104) Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTAccellion FTA versions 9_12_370 and earlier
Unauthenticated remote attackers can execute arbitrary OS commands and gain full system control by sending crafted POST requests to various admin endpoints
Immediately upgrade to Accellion FTA version 9_12_380 or later, or migrate to a supported secure file transfer platform
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Immediately upgrade the appliance to Accellion FTA version 9_12_380 or later. Apply the update package via the administrative console as follows:
# Access the FTA administrative console and trigger the update to the patched version
# (Note: Command syntax may vary depending on your specific appliance deployment model)
appliance_control --update --version 9_12_3802. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, restrict external access to all administrative endpoints. Implement strict IP-based access control lists (ACLs) on your reverse proxy or firewall.
# Example Nginx configuration to restrict access to administrative endpoints
server {
listen 443 ssl;
server_name fta.example.com;
# Block external access to admin/support endpoints and allow only trusted internal subnets
location ~* ^/(admin|supp)/ {
allow 10.0.0.0/8;
allow 192.168.0.0/16;
deny all;
proxy_pass http://127.0.0.1:8080;
}
}3. Log Audit & IoC Verification Commands
Use the following commands to verify the installed software version and inspect web server logs for potential exploitation attempts.
# 1. Check the currently installed Accellion FTA package version
rpm -qa | grep -i accellion
# 2. Scan web access logs for suspicious POST requests targeting admin endpoints
grep -Ei 'POST /(admin|supp)/' /var/log/apache2/access.log /var/log/nginx/access.log | grep -E 'eval|system|sh|bash'Block Exploits Instantly with Managed Virtual Patching Rules
Can't patch production immediately? Deploy managed WAF rules at the edge to intercept RCE, SQLi, and deserialization payloads before they hit your origin server.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2021-27104) is an OS Command Injection vulnerability (CWE-78) residing in the administrative endpoints of Accellion FTA (File Transfer Appliance). The root cause is the lack of proper input validation and sanitization of parameters passed within HTTP POST requests, allowing untrusted user input to be executed directly by the system shell.
2. Exploitation Mechanics & Attack Scenario
An unauthenticated attacker can exploit this vulnerability by sending a specially crafted HTTP POST request targeting administrative endpoints. The malicious payload embedded in the request is processed by the backend scripts and executed with administrative privileges on the underlying operating system. In real-world attacks, this vector has been actively exploited to deploy web shells, establish persistence, and exfiltrate sensitive data.
3. Infrastructure & Business Impact
With a CVSS score of 9.8 (Critical) and its inclusion in the CISA Known Exploited Vulnerabilities (KEV) catalog, this vulnerability poses an extreme risk. Successful exploitation allows complete compromise of the appliance, leading to unauthorized access to highly sensitive files transferred via the platform, potential lateral movement within the corporate network, and severe reputational damage.
Official Vendor Advisories & References
Accellion FTA 9_12_370 and earlier is affected by OS command execution via a crafted POST request to various admin endpoints. The fixed version is FTA_9_12_380 and later.
Frequently Asked SecOps Questions (CVE-2021-27104)
FAQQ1. How critical is CVE-2021-27104 and is it actively exploited in the wild?
CVE-2021-27104 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 56.7%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-27104?
Primary impacted vendors include accellion across fta. Scope summary: All Accellion FTA versions 9_12_370 and earlier
Q3. What temporary mitigations or workarounds exist for CVE-2021-27104 before patching?
[Mitigation] Immediately upgrade to Accellion FTA version 9_12_380 or later, or migrate to a supported secure file transfer platform Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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