CVE-2020-13920: Apache ActiveMQ Auth Bypass Vulnerability

CVE-2020-13920 Overview

Apache ActiveMQ contains a man-in-the-middle vulnerability in its JMX RMI registry implementation. The vulnerability exists because Apache ActiveMQ uses LocateRegistry.createRegistry() to create the JMX RMI registry and binds the server to the "jmxrmi" entry without proper authentication controls. An attacker can connect to the registry without authentication and call the rebind method to rebind jmxrmi to a malicious proxy server, enabling credential interception when legitimate users connect.

Critical Impact

Attackers can intercept administrative credentials by exploiting unauthenticated JMX RMI registry access, potentially leading to complete compromise of ActiveMQ message broker infrastructure.

Affected Products

• Apache ActiveMQ (versions prior to 5.15.12)
• Oracle Communications Diameter Signaling Router
• Oracle FLEXCUBE Private Banking 12.0.0 and 12.1.0
• Debian Linux 9.0

Discovery Timeline

• September 10, 2020 - CVE-2020-13920 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-13920

Vulnerability Analysis

This vulnerability stems from a missing authentication mechanism (CWE-306) in Apache ActiveMQ's JMX RMI registry implementation. The JMX (Java Management Extensions) interface is designed to allow administrators to monitor and manage ActiveMQ brokers. However, the registry creation process lacks proper access controls, allowing unauthenticated network connections.

The vulnerability enables a sophisticated man-in-the-middle attack scenario. When an administrator attempts to connect to the JMX interface for management purposes, they expect to communicate directly with the ActiveMQ server. However, an attacker who has previously exploited this vulnerability can intercept these connections through a proxy server bound to the jmxrmi entry, capturing authentication credentials transmitted during the connection handshake.

Root Cause

The root cause lies in the use of LocateRegistry.createRegistry() without implementing authentication requirements on the RMI registry. This allows any network-accessible client to invoke the rebind method, effectively replacing the legitimate jmxrmi binding with an attacker-controlled endpoint. The lack of authentication on registry operations violates the principle of least privilege and exposes critical management interfaces to unauthorized manipulation.

Attack Vector

The attack leverages network-accessible JMX RMI services to execute a man-in-the-middle attack:

1. Reconnaissance: The attacker identifies an exposed ActiveMQ JMX RMI registry on the network
2. Registry Manipulation: Without authentication, the attacker connects to the RMI registry and calls the rebind method
3. Proxy Setup: The attacker creates a malicious RMI server that proxies requests to the original jmxrmi service
4. Credential Interception: When legitimate administrators connect to manage ActiveMQ, their credentials pass through the attacker's proxy server
5. Exploitation: Captured credentials can be used for unauthorized access to the ActiveMQ broker and potentially lateral movement within the network

The attack requires network access to the JMX RMI port (typically port 1099) and high complexity due to the need to set up a functioning proxy server. However, no privileges or user interaction are required for successful exploitation.

Detection Methods for CVE-2020-13920

Indicators of Compromise

• Unexpected rebind operations in RMI registry logs indicating potential registry manipulation
• Multiple JMX connections from unusual IP addresses or at irregular times
• Network traffic analysis showing JMX communications routing through unexpected intermediary hosts
• Authentication failures followed by successful connections from different source addresses

Detection Strategies

• Monitor RMI registry operations for unauthorized rebind calls, particularly targeting the "jmxrmi" entry
• Implement network segmentation monitoring to detect JMX traffic crossing unexpected boundaries
• Deploy intrusion detection rules to identify RMI registry manipulation patterns
• Correlate JMX authentication logs with network flow data to identify proxy interception scenarios

Monitoring Recommendations

• Enable detailed logging for all JMX RMI registry operations on ActiveMQ brokers
• Implement network traffic monitoring on JMX ports (default 1099) to baseline normal administrative access patterns
• Configure alerts for any rebind operations on the jmxrmi registry entry
• Monitor for new or unexpected SSL/TLS certificates presented during JMX connections

How to Mitigate CVE-2020-13920

Immediate Actions Required

• Upgrade Apache ActiveMQ to version 5.15.12 or later immediately
• Restrict network access to JMX RMI ports using firewall rules to allow only authorized management hosts
• Implement network segmentation to isolate ActiveMQ management interfaces from untrusted networks
• Review JMX access logs for any signs of prior exploitation or unauthorized access attempts

Patch Information

Apache has released a security patch in Apache ActiveMQ version 5.15.12 that addresses this vulnerability. The fix implements proper authentication controls on the JMX RMI registry to prevent unauthorized rebind operations. Organizations should upgrade to this version or later to remediate the vulnerability. Additional vendor patches are available:

• Apache ActiveMQ Security Advisory
• Oracle Critical Patch Update for Oracle products
• Debian LTS Security Announcement for Debian systems

Workarounds

• Disable JMX remote access entirely if not required for operational purposes
• Implement SSL/TLS for JMX connections using the -Dcom.sun.management.jmxremote.ssl=true option
• Configure JMX authentication using password files with the -Dcom.sun.management.jmxremote.authenticate=true option
• Use VPN or SSH tunneling to secure JMX management access from authorized administrative workstations

# Configuration example - Securing JMX in ActiveMQ
# Add to activemq.xml or ACTIVEMQ_OPTS in env configuration

# Enable JMX authentication
export ACTIVEMQ_OPTS="$ACTIVEMQ_OPTS -Dcom.sun.management.jmxremote.authenticate=true"
export ACTIVEMQ_OPTS="$ACTIVEMQ_OPTS -Dcom.sun.management.jmxremote.ssl=true"
export ACTIVEMQ_OPTS="$ACTIVEMQ_OPTS -Dcom.sun.management.jmxremote.password.file=/path/to/jmxremote.password"
export ACTIVEMQ_OPTS="$ACTIVEMQ_OPTS -Dcom.sun.management.jmxremote.access.file=/path/to/jmxremote.access"

# Restrict JMX to localhost only if remote access not needed
export ACTIVEMQ_OPTS="$ACTIVEMQ_OPTS -Djava.rmi.server.hostname=127.0.0.1"