CVE-2020-27131: Cisco Security Manager RCE Vulnerability

CVE-2020-27131 Overview

Multiple vulnerabilities in the Java deserialization function used by Cisco Security Manager could allow an unauthenticated, remote attacker to execute arbitrary commands on an affected device. These vulnerabilities are due to insecure deserialization of user-supplied content by the affected software. An attacker could exploit these vulnerabilities by sending a malicious serialized Java object to a specific listener on an affected system. A successful exploit could allow the attacker to execute arbitrary commands on the device with the privileges of NT AUTHORITY\SYSTEM on the Windows target host.

Critical Impact

Unauthenticated remote attackers can achieve complete system compromise with SYSTEM-level privileges through malicious Java object deserialization, with no patch currently available from Cisco.

Affected Products

• Cisco Security Manager (all versions)

Discovery Timeline

• 2020-11-17 - CVE-2020-27131 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-27131

Vulnerability Analysis

This vulnerability falls under the category of Insecure Deserialization (CWE-502) combined with Improper Input Validation (CWE-20). The affected Cisco Security Manager application fails to properly validate or sanitize serialized Java objects received from external sources before deserializing them. When the application processes a specially crafted serialized Java object, it can instantiate arbitrary classes and execute their methods during the deserialization process.

The exploitation requires no authentication, making this vulnerability particularly dangerous in enterprise environments where Cisco Security Manager is deployed. The attacker needs only network access to the vulnerable listener to deliver the malicious payload. Upon successful exploitation, the attacker gains command execution capabilities with the highest privilege level on Windows systems (NT AUTHORITY\SYSTEM), enabling complete system compromise including data exfiltration, lateral movement, and persistent access.

Root Cause

The root cause stems from insecure handling of Java object deserialization within Cisco Security Manager. The application deserializes user-supplied content without implementing proper type checking, allowlist filtering, or isolation mechanisms. This allows an attacker to include malicious gadget chains within serialized objects that, when deserialized, trigger the execution of arbitrary system commands. The lack of input validation on the deserialization interface permits untrusted data to influence the application's execution flow.

Attack Vector

The attack is conducted over the network and requires no user interaction or prior authentication. An attacker identifies a vulnerable Cisco Security Manager installation and sends a specially crafted HTTP request containing a malicious serialized Java object to the application's listener. The serialized object contains a gadget chain—a sequence of Java class method invocations that ultimately lead to command execution. When the server deserializes this object, the gadget chain executes, running attacker-controlled commands with SYSTEM privileges.

The vulnerability mechanism involves crafting a serialized Java object that leverages known gadget chains (such as those found in common Java libraries) to achieve arbitrary command execution. The malicious object is transmitted to the vulnerable service endpoint, where the deserialization process triggers the exploit chain. For detailed technical information, refer to the Cisco Security Advisory.

Detection Methods for CVE-2020-27131

Indicators of Compromise

• Unusual network connections to Cisco Security Manager service ports from external or untrusted IP addresses
• Unexpected process spawning from the Java runtime environment running Cisco Security Manager
• Evidence of cmd.exe or powershell.exe processes executing with NT AUTHORITY\SYSTEM privileges as children of Java processes
• Suspicious serialized Java object signatures in network traffic (magic bytes ac ed 00 05)

Detection Strategies

• Deploy network intrusion detection rules to identify Java serialization magic bytes (0xaced0005) in HTTP traffic destined for Cisco Security Manager
• Monitor for known Java deserialization gadget chain class names in network payloads (e.g., org.apache.commons.collections.functors.InvokerTransformer)
• Implement endpoint detection for anomalous process creation patterns where Java processes spawn system shells

Monitoring Recommendations

• Enable verbose logging on Cisco Security Manager and forward logs to a SIEM for correlation analysis
• Monitor Windows Security Event Logs (Event ID 4688) for process creation events associated with the Cisco Security Manager service account
• Implement network traffic analysis to detect serialized Java objects in inbound HTTP requests

How to Mitigate CVE-2020-27131

Immediate Actions Required

• Restrict network access to Cisco Security Manager to only trusted management networks and IP addresses
• Implement firewall rules to block external access to the vulnerable service listeners
• Consider isolating the Cisco Security Manager server in a dedicated network segment with strict access controls
• Evaluate alternative solutions if continued use of Cisco Security Manager is required

Patch Information

Cisco has not released software updates that address these vulnerabilities. Organizations should implement compensating controls and workarounds until an official patch becomes available. Monitor the Cisco Security Advisory for updates regarding patch availability.

Workarounds

• Implement strict network segmentation to limit access to Cisco Security Manager from trusted hosts only
• Deploy a Web Application Firewall (WAF) capable of inspecting and blocking malicious serialized Java objects
• Consider deploying Runtime Application Self-Protection (RASP) solutions to detect deserialization attacks
• Regularly review access logs and security events for signs of exploitation attempts

# Example firewall rule to restrict access to Cisco Security Manager (adjust ports and IPs as needed)
# Windows Firewall - Allow only management subnet
netsh advfirewall firewall add rule name="CSM Restrict Access" dir=in action=allow protocol=tcp localport=443 remoteip=10.0.0.0/24
netsh advfirewall firewall add rule name="CSM Block External" dir=in action=block protocol=tcp localport=443 remoteip=any