Detect Network Device Authentication in Splunk
Adversaries may patch network device operating systems to add a hardcoded backdoor password, bypassing normal authentication for local accounts on routers, switches, and VPN appliances. SYNful Knock implanted a backdoor password in Cisco IOS router images, checking if login credentials match the backdoor password before passing them to normal authentication. SLOWPULSE modified Pulse Secure LDAP and 2FA authentication to accept a designated attacker-supplied password. Detection relies on network configuration integrity checks and unusual authentication behavior.
MITRE ATT&CK
- Technique
- T1556 Modify Authentication Process
- Sub-technique
- T1556.004 Network Device Authentication
- Canonical reference
- https://attack.mitre.org/techniques/T1556/004/
SPL Detection Query
index=network_syslog OR index=cisco_logs
sourcetype IN ("cisco:ios", "cisco:asa", "juniper:junos", "paloalto:firewall")
| eval AuthResult=case(
match(lower(_raw), "(authentication succeeded|login successful|accepted password|authenticated)"), "SUCCESS",
match(lower(_raw), "(authentication failed|incorrect password|bad password|login failed|access denied)"), "FAILURE",
1==1, "OTHER"
)
| where AuthResult IN ("SUCCESS", "FAILURE")
| rex field=_raw "(?:from|src)\s+(?<src_ip>\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})"
| rex field=_raw "(?:user|username|for)\s+(?<user>\S+)"
| stats count as Events, countif(AuthResult="SUCCESS") as Successes,
countif(AuthResult="FAILURE") as Failures, dc(user) as UniqueUsers
by host, src_ip, span(_time, 1h)
| eval SuccessRate=round(Successes/(Events+0.001)*100, 1)
| where Failures > 5 OR (UniqueUsers > 3 AND Successes > 0)
| sort - EventsDetects anomalous authentication patterns on network devices (Cisco IOS, ASA, Juniper JunOS, Palo Alto) using vendor-specific syslog sourcetypes. Calculates per-hour success/failure ratios and unique user counts per source IP to surface backdoor password testing or successful bypass attempts.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Network management systems generating authentication events during scheduled device polls
- Legitimate multi-account administrative sessions from the same management workstation
- Device reboots causing reauthentication events from multiple monitoring systems simultaneously
- Syslog rate-limiting causing bunched events that appear as spikes
Other platforms for T1556.004
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Verify Cisco IOS Image Hash (Integrity Check)
Expected signal: SSH authentication event in network device syslog. Network device syslog entry for privileged exec command execution. If syslog forwarding is configured, Splunk/Sentinel will capture the authentication and command events.
- Test 2Simulate Failed Network Device Authentication (Syslog Testing)
Expected signal: Network device syslog entries: 'Authentication failed for user testuser from <IP>'. If forwarded to SIEM: Splunk index=network_syslog with authentication failure events. Five events in rapid succession should trigger the failure rate detection.
- Test 3Check Network Device Syslog Collection
Expected signal: Test syslog message appearing in SIEM with source IP of the test host. The message mimics a Cisco IOS login success event and should match the network device authentication detection patterns.
References (5)
- https://attack.mitre.org/techniques/T1556/004/
- https://cloud.google.com/blog/topics/threat-intelligence/synful-knock-acis/
- https://tools.cisco.com/security/center/resources/integrity_assurance.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1556.004/T1556.004.md
- https://www.mandiant.com/resources/blog/mandiant-identifies-new-pulse-connect-secure-vulnerabilities
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