Service

IKE

IKE negotiates IPsec VPN tunnels. Attackers enumerate transform sets, fingerprint vendors, exploit aggressive mode to capture PSKs, and crack weak credentials to gain VPN access

:4500 8 guides 3 phases

1 min read Created: Feb 21, 2026 Updated: Jul 14, 2026

IKE (Internet Key Exchange) is the protocol used to set up IPsec VPN tunnels. It runs on UDP port 500 for standard negotiation and UDP port 4500 for NAT traversal (NAT-T). Nmap identifies the service as isakmp. IKE exists in two versions: IKEv1 and IKEv2, each with different security properties.

VPN gateways are high-value targets because they provide direct network access when compromised. IKEv1 Aggressive Mode leaks the group name (pre-shared key identifier) in cleartext, enabling offline brute-forcing of the pre-shared key. Weak or default pre-shared keys, outdated encryption proposals (DES, MD5), and known vendor-specific vulnerabilities are common findings on VPN appliances from Cisco, Fortinet, and others.

Enumeration starts with ike-scan to fingerprint the VPN gateway, determine the IKE version, identify supported transforms, and detect Aggressive Mode. Nmap's ike-version script provides similar information. Once a valid transform set is identified, testing for weak pre-shared keys and attempting to establish a tunnel are the next steps. Tools like ikeforce automate group name enumeration and PSK cracking.