Accellion FTA OS Command Execution via Local Web Service Call (CVE-2021-27102) Technical Analysis and Hardening Guide
Executive & SecOps Summary
SECOPS ASSESSMENTAccellion FTA 9_12_411 and earlier
Local attackers or compromised processes can execute arbitrary OS commands via local web service calls, leading to full system compromise
Immediately upgrade Accellion FTA to version FTA_9_12_416 or later
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Administrators must immediately upgrade the appliance to FTA_9_12_416 or later. Use the following administrative commands to check and apply the update:
# Verify the current version of the Accellion FTA appliance
cat /home/seos/courier/about.html | grep -i 'version'
# Check and apply the official update package
# (Ensure appropriate licensing and network access are configured)
/home/seos/bin/ftaupdate --check
/home/seos/bin/ftaupdate --install FTA_9_12_4162. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, restrict access to the local web services using host-based firewall rules to prevent unauthorized local or remote loopback exploitation.
# Restrict access to the local web service port (e.g., port 8080) to trusted local processes only
iptables -A INPUT -p tcp -s 127.0.0.1 --dport 8080 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP
# Save and restart the iptables service to apply changes
service iptables save
service iptables restart3. Log Audit & IoC Verification Commands
Run the following commands to inspect web server and system logs for potential indicators of compromise (IoCs) related to command injection attempts.
# Scan web server access logs for common shell metacharacters and command execution patterns
grep -E '(\;|\||\&|\`|\$\()' /var/log/apache2/access.log /var/log/nginx/access.log 2>/dev/null
# Audit system logs for suspicious processes spawned by the web server user (e.g., apache, www-data)
grep -E '(sh|bash|perl|python|curl|wget)' /var/log/secure /var/log/audit/audit.log 2>/dev/nullBlock Exploits Instantly with Managed Virtual Patching Rules
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
CVE-2021-27102 is an OS command injection vulnerability (CWE-78) residing within the local web service component of Accellion FTA (File Transfer Appliance). The root cause lies in the insufficient sanitization of input parameters passed to internal web service calls. When these unvalidated inputs are concatenated directly into system shell execution functions, it allows an attacker with local access or the ability to trigger internal web requests to execute arbitrary operating system commands.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by sending a crafted request containing shell metacharacters (such as ';', '|', or '&') to the vulnerable local web service endpoint. Because the application processes this request with elevated privileges and executes it via a system shell, the injected commands run under the context of the web server or administrative user. This vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, highlighting its active exploitation by threat actors for initial access and data exfiltration.
3. Infrastructure & Business Impact
Since Accellion FTA is typically deployed at the network perimeter to facilitate secure file transfers, successful exploitation poses an extreme risk to enterprise data confidentiality. Attackers can exfiltrate sensitive files, deploy web shells for persistent access, and pivot into the internal corporate network, resulting in severe reputational damage, regulatory non-compliance, and operational disruption.
Official Vendor Advisories & References
Accellion FTA 9_12_411 and earlier is affected by OS command execution via a local web service call. The fixed version is FTA_9_12_416 and later.
Frequently Asked SecOps Questions (CVE-2021-27102)
FAQQ1. How critical is CVE-2021-27102 and is it actively exploited in the wild?
CVE-2021-27102 is rated CVSS 7.8 (HIGH) with a 30-day EPSS exploitation probability of 3.6%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-27102?
Primary impacted vendors include accellion across fta. Scope summary: Accellion FTA versions 9_12_411 and earlier (All versions prior to FTA_9_12_416)
Q3. What temporary mitigations or workarounds exist for CVE-2021-27102 before patching?
[Mitigation] Immediately upgrade Accellion FTA to version FTA_9_12_416 or later Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2021-27102
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
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