Cisco Secure Access Control System (ACS) Java Deserialization Remote Code Execution (CVE-2018-0147)
Executive & SecOps Summary
SECOPS ASSESSMENTCisco Secure Access Control System (ACS) prior to release 5.8 Patch 9
An unauthenticated, remote attacker can execute arbitrary commands on the affected device with root privileges by sending a crafted serialized Java object
Immediately upgrade to Cisco ACS 5.8 Patch 9 or later, or restrict network access to vulnerable ports
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
According to Cisco's official advisory, administrators must upgrade to ACS 5.8 Patch 9 or later. Use the following CLI commands to apply the patch:
# Download and install the patch from your configured repository
acs patch install acs-5.8.0.32.9-patch.tar.gpg repository <your_repository_name>
# Verify the installed version and patch level
show version2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, restrict network access to the ACS management interfaces and Java-related ports using Access Control Lists (ACLs) on your firewall or upstream router.
# Example ACL to block untrusted traffic to ACS (e.g., 192.168.10.50) on common Java serialization ports
ip access-list extended BLOCK_UNTRUSTED_ACS
deny tcp any host 192.168.10.50 eq 8000
deny tcp any host 192.168.10.50 eq 1099
permit ip any any3. Log Audit & IoC Verification Commands
Monitor the ACS logs for unexpected Java deserialization exceptions or unauthorized root command executions.
# Search for Java deserialization errors and suspicious ObjectInputStream activities in ACS logs
grep -rn 'ObjectInputStream' /opt/CSCOacs/logs/
grep -ri 'java.io.InvalidClassException' /opt/CSCOacs/logs/Stop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2018-0147) is a critical Java deserialization flaw in Cisco Secure Access Control System (ACS). The root cause lies in the insecure deserialization of user-supplied content by the affected software (CWE-502). Because the application fails to properly validate or sanitize serialized Java objects before reconstructing them in memory, an attacker can force the application to execute arbitrary code.
2. Exploitation Mechanics & Attack Scenario
An attacker targets specific TCP ports used by Cisco ACS for Java-based communication (such as RMI, JMX, or HTTP-based serialization endpoints). By utilizing known gadget chains (e.g., Apache Commons Collections), the attacker crafts a malicious serialized Java object containing system commands. When this payload is transmitted to the target ACS server, the Java Virtual Machine (JVM) deserializes the object, triggering the execution of the embedded payload with root privileges without requiring any authentication.
3. Infrastructure & Business Impact
Cisco ACS is a core security infrastructure component responsible for network access control (TACACS+/RADIUS). This vulnerability has a CVSS score of 9.8 (Critical) and is listed in the CISA KEV (Known Exploited Vulnerabilities) catalog. Successful exploitation allows an attacker to gain full root-level access to the ACS appliance, enabling them to compromise the entire network authentication infrastructure and pivot deeper into the internal network.
Official Vendor Advisories & References
A vulnerability in Java deserialization used by Cisco Secure Access Control System (ACS) prior to release 5.8 patch 9 could allow an unauthenticated, remote attacker to execute arbitrary commands on an affected device. The vulnerability is due to insecure deserialization of user-supplied content by the affected software. An attacker could exploit this vulnerability by sending a crafted serialized Java object. An exploit could allow the attacker to execute arbitrary commands on the device with root privileges. Cisco Bug IDs: CSCvh25988.
Frequently Asked SecOps Questions (CVE-2018-0147)
FAQQ1. How critical is CVE-2018-0147 and is it actively exploited in the wild?
CVE-2018-0147 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 18.2%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2018-0147?
Primary impacted vendors include cisco across secure_access_control_system. Scope summary: All versions of Cisco Secure Access Control System (ACS) prior to release 5.8 Patch 9 (Cisco Bug ID: CSCvh25988)
Q3. What temporary mitigations or workarounds exist for CVE-2018-0147 before patching?
[Mitigation] Immediately upgrade to Cisco ACS 5.8 Patch 9 or later, or restrict network access to vulnerable ports Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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