Detect VPN and Remote Access Credential Stuffing / Brute Force in Elastic Security
Credential stuffing and brute force against VPN and remote access gateways is a persistent initial access vector for ransomware operators and nation-state actors. NCSC and CISA have repeatedly warned about Fortinet, Cisco ASA/FTD, Ivanti Connect Secure, Palo Alto GlobalProtect, and SonicWall VPN gateways being targeted. Attackers use credential databases from prior breaches and automated tools to test credentials at scale against VPN login portals. Unlike password spraying against M365, VPN credential stuffing often targets a single account at high frequency (bypassing account lockout through IP rotation) or uses a large pool of breached credential pairs. Volt Typhoon (China-nexus) specifically targets small business routers and VPN gateways for SOHO Living-off-the-Land access. Compromised VPN access gives attackers direct network access, bypassing perimeter defences entirely.
MITRE ATT&CK
- Tactic
- Credential Access Initial Access
Elastic Detection Query
sequence by source.ip with maxspan=15m
[network where event.dataset in ("cisco_asa.log", "fortinet.firewall", "paloalto_cortex.xdr") and
event.outcome == "failure" and
event.action : ("vpn*", "remote-access*", "ssl-vpn*")] with runs=20
[network where event.dataset in ("cisco_asa.log", "fortinet.firewall", "paloalto_cortex.xdr") and
event.outcome == "success" and
event.action : ("vpn*", "remote-access*", "ssl-vpn*")]EQL sequence: 20+ VPN authentication failures from same IP followed by a success — the credential stuffing to compromise pattern.
Data Sources
Required Tables
False Positives & Tuning
- Password change causing brief retry surge then success
Other platforms for THREAT-VPN-CredentialStuffing
Testing Methodology
Validate this detection against 1 adversary technique 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 1VPN Credential Stuffing Simulation via Python Requests
Expected signal: VPN authentication logs record multiple failures (error: invalid credentials) for multiple usernames from the test IP within the 15-minute window.
References (5)
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