Detection of Suspicious Cisco Configuration Changes via Archive Logging

This threat brief focuses on detecting malicious activity within Cisco IOS devices by analyzing configuration archive logs. Configuration archive logging captures all modifications made to a device’s configuration, offering a detailed audit trail. Analyzing these logs allows for the identification of suspicious or malicious activities, such as the creation of backdoor accounts, modifications to SNMP community strings, and the setup of TFTP servers for potential data exfiltration. This detection method is crucial for identifying advanced attack campaigns, exemplified by threat actors like Static Tundra, who often manipulate network configurations to maintain persistence and facilitate lateral movement. The monitoring of configuration changes across different user sessions provides a comprehensive view of device activity.

Attack Chain

1. Attacker gains initial access to the network through an external vulnerability or compromised credentials.
2. Attacker leverages their initial access to authenticate to a Cisco IOS device.
3. The attacker modifies the device configuration to create a new user account with privilege level 15, effectively creating a backdoor.
4. The attacker changes the SNMP community string to gain unauthorized access to network monitoring data.
5. The attacker configures a TFTP server on the Cisco device to enable data exfiltration.
6. The attacker modifies the user table to elevate privileges of existing accounts.
7. The attacker uses the elevated privileges to move laterally within the network.
8. The attacker exfiltrates sensitive data using the configured TFTP server.

Impact

Compromised Cisco IOS devices can lead to significant network breaches, data exfiltration, and persistent access for malicious actors. Successful exploitation allows attackers to move laterally within the network, gain access to sensitive data, and maintain a foothold for future attacks. The CVE-2018-0171 vulnerability, related to Cisco Smart Install, can allow remote code execution, potentially impacting thousands of devices if not properly patched. Unauthorized configuration changes can disrupt network operations, compromise sensitive data, and damage an organization’s reputation.

Recommendation

• Enable Cisco IOS archive logging with the commands archive and log config in global configuration mode to generate the necessary logs for detection.
• Configure command logging with archive log config logging enable and set appropriate logging levels with logging trap informational on Cisco devices to capture configuration changes.
• Deploy the Sigma rule “Cisco Privilege Escalation via Configuration Change” to detect the creation of high-privilege accounts (All_Changes.command="usernameprivilege 15*").
• Deploy the Sigma rule “Cisco SNMP Community String Modification” to identify unauthorized changes to SNMP settings (All_Changes.command="snmp-server community").
• Investigate any alerts generated by the Sigma rules, focusing on the source device (dest) and the user (user) involved, using the provided drilldown searches.
• Monitor logs for CVE-2018-0171 and apply necessary patches.