CVE-2021-21307: Lucee Server RCE Vulnerability

CVE-2021-21307 Overview

CVE-2021-21307 is a critical unauthenticated remote code execution vulnerability affecting Lucee Server, a dynamic Java-based (JSR-223) tag and scripting language platform used for rapid web application development. The vulnerability exists in the Lucee Admin interface, where missing authorization controls allow unauthenticated attackers to execute arbitrary code on vulnerable systems without requiring any user interaction or prior authentication.

Critical Impact

This vulnerability allows unauthenticated attackers to achieve complete system compromise through remote code execution on Lucee Server installations. Attackers can gain full control over affected web applications and underlying server infrastructure.

Affected Products

• Lucee Server versions prior to 5.3.7.47
• Lucee Server versions prior to 5.3.6.68
• Lucee Server versions prior to 5.3.5.96

Discovery Timeline

• 2021-02-11 - CVE-2021-21307 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-21307

Vulnerability Analysis

This vulnerability stems from missing authorization checks (CWE-862) in the Lucee Administrator interface. The flaw allows unauthenticated remote attackers to access administrative functionality that should require authentication. The vulnerability is exploitable over the network without requiring any privileges or user interaction, enabling complete compromise of confidentiality, integrity, and availability of affected systems.

The vulnerability was notably used in real-world security research, with researchers demonstrating its impact against high-profile targets. The PortSwigger security research article documents how this vulnerability was discovered during research on Apple's travel portal infrastructure.

Root Cause

The root cause is a Missing Authorization vulnerability (CWE-862) in the Lucee Admin application. Before the patch, the application failed to verify whether a user was authenticated before allowing access to sensitive administrative endpoints. Specifically, the Application.cfc file lacked proper session validation checks, allowing unauthenticated users to access files beyond the main login pages (admin.cfm, web.cfm, server.cfm).

Attack Vector

The attack vector is network-based, targeting the Lucee Administrator interface which is typically accessible via HTTP/HTTPS. An attacker can remotely access administrative functions including file operations through endpoints like imgProcess.cfm, which can be exploited for arbitrary file write operations leading to remote code execution. The Packet Storm Exploit provides detailed technical information about the exploitation methodology.

The following patch was applied to address the vulnerability by implementing session validation in the onRequestStart() function:

 this.sessionCookie.sameSite = "strict";
 this.tag.cookie.sameSite = "strict";
 
+public function onRequestStart() {
+	// if not logged in, we only allow access to admin|web|server[.cfm]
+	if(!structKeyExists(session, "passwordWeb") && !structKeyExists(session, "passwordServer")){
+		var fileName=listLast(cgi.script_name,"/");
+		if(fileName!="admin.cfm" && fileName!="web.cfm" && fileName!="server.cfm") {
+			cfheader(statuscode="404" statustext="Invalid access");
+        	abort;
+		}
+	}
+}
+
 public function onApplicationStart(){
 	if(structKeyExists(server.system.environment,"LUCEE_ADMIN_ENABLED") && server.system.environment.LUCEE_ADMIN_ENABLED EQ false){
 		cfheader(statuscode="404" statustext="Invalid access");

Source: GitHub Lucee Commit

Detection Methods for CVE-2021-21307

Indicators of Compromise

• Unexpected HTTP requests to Lucee Administrator endpoints from external IP addresses, particularly to imgProcess.cfm
• Web server logs showing access to administrative CFM files without corresponding authentication events
• Newly created or modified files in the Lucee webroot or web-accessible directories
• Unusual Java process activity or spawned child processes from the Lucee Server process

Detection Strategies

• Monitor web server access logs for requests to /lucee/admin/ paths from unauthorized sources
• Implement Web Application Firewall (WAF) rules to detect and block exploitation attempts targeting Lucee Admin endpoints
• Configure intrusion detection systems to alert on patterns consistent with arbitrary file write attempts
• Review file integrity monitoring alerts for unexpected modifications in Lucee installation directories

Monitoring Recommendations

• Enable detailed logging on the Lucee Server to capture all administrative access attempts
• Deploy network traffic analysis to identify reconnaissance and exploitation attempts against Lucee installations
• Implement real-time alerting for any access to the Lucee Administrator from non-whitelisted IP addresses
• Monitor system processes for suspicious activity originating from the Java/Lucee runtime

How to Mitigate CVE-2021-21307

Immediate Actions Required

• Update Lucee Server immediately to version 5.3.7.47, 5.3.6.68, or 5.3.5.96 or later
• Block external access to the Lucee Administrator interface until patching is complete
• Review server logs for any indicators of prior exploitation attempts
• Conduct a security assessment of systems that may have been exposed

Patch Information

Lucee has released patched versions that address this vulnerability. The fix introduces proper session validation in the onRequestStart() function of Application.cfc, ensuring that unauthenticated users can only access the main login pages. Organizations should upgrade to one of the following fixed versions:

• Lucee 5.3.7.47 or later (for 5.3.7.x branch)
• Lucee 5.3.6.68 or later (for 5.3.6.x branch)
• Lucee 5.3.5.96 or later (for 5.3.5.x branch)

The security patch is documented in the GitHub Security Advisory and the Lucee Vulnerability Alert.

Workarounds

• Block access to the Lucee Administrator interface entirely from external networks using firewall rules
• Implement network-level access controls to restrict Lucee Admin access to trusted internal IP addresses only
• Configure web server rules to deny access to /lucee/admin/ paths from untrusted sources
• Consider disabling the Lucee Administrator in production environments using the LUCEE_ADMIN_ENABLED environment variable

# Example Apache configuration to block Lucee Admin access
<LocationMatch "^/lucee/admin/">
    Require ip 10.0.0.0/8
    Require ip 192.168.0.0/16
    Require ip 172.16.0.0/12
</LocationMatch>

# Example nginx configuration
location /lucee/admin/ {
    allow 10.0.0.0/8;
    allow 192.168.0.0/16;
    allow 172.16.0.0/12;
    deny all;
}