UDP Remote Access

Port 4500 (IPSec NAT-T)

Learn about port 4500 (IPSec NAT-T) - security risks, vulnerabilities, and common uses. Find devices with port 4500 open.

Quick Info

Port Number

4500

Protocol

UDP

Service

IPSec NAT-T

IANA Name

IPSec NAT-T

Service Description

UDP port 4500 is primarily used for IPsec NAT Traversal (NAT-T). When IPsec (Internet Protocol Security) VPN tunnels pass through Network Address Translation (NAT) devices, the original IPsec headers are often modified, which can break the tunnel. NAT-T encapsulates the IPsec packets within UDP datagrams on port 4500, allowing them to traverse NAT devices without being corrupted. This encapsulation allows IPsec to function correctly even when the client or server is behind a NAT device. The protocol works by detecting the presence of a NAT device along the path. If a NAT is detected, both endpoints agree to encapsulate the IPsec traffic within UDP packets destined for port 4500. The encapsulated packets are then transmitted, and the receiving end decapsulates them before processing the IPsec payload. The use of UDP allows NAT devices to maintain state about the connection and forward traffic correctly. The specific encapsulation format is defined in RFC 3947.

## Firewall Recommendations

Blocking UDP port 4500 will prevent IPsec VPNs from functioning when NAT is present. If you are not using IPsec VPNs that need to traverse NAT, blocking this port can reduce the attack surface. If you require IPsec VPN functionality behind NAT, ensure that UDP port 4500 is allowed through the firewall. Best practices include restricting access to this port to only trusted IP addresses or networks, using strong encryption algorithms and authentication methods for IPsec, and keeping the IPsec implementation and firewall software up to date with the latest security patches. Intrusion detection systems should be configured to monitor traffic on port 4500 for suspicious activity.

Security Information

While IPsec with NAT-T is generally considered secure, vulnerabilities can arise from misconfigurations or weaknesses in the underlying IPsec implementation. If IPsec is not properly configured with strong encryption algorithms and authentication methods, the data transmitted within the VPN tunnel can be vulnerable to interception and decryption. Attackers might target port 4500 to attempt to exploit vulnerabilities in the IPsec implementation or to perform denial-of-service attacks. Additionally, if the NAT device itself has vulnerabilities, it could be exploited to compromise the IPsec tunnel. Rogue IPsec implementations could be used to establish tunnels and exfiltrate data. The port itself isn't inherently vulnerable, but it acts as a gateway to the underlying IPsec protocols, thus any vulnerabilities within the IPsec protocol can be targeted through port 4500.

Known Vulnerabilities

CVE	Name	Severity	Description
CVE-2018-5394	FragmentSmack	High	Уязвимость типа отказ в обслуживании (DoS) в ядре Linux, влияющая на обработку фрагментированных IP пакетов, что может быть использовано для истощения ресурсов CPU.
CVE-2017-17492	StrongSwan EAP Authentication Bypass	Medium	Уязвимость в StrongSwan, позволяющая обойти аутентификацию EAP, если используется определенная конфигурация.
CVE-2015-4081	Libreswan IKEv1 Aggressive Mode Vulnerability	Medium	Уязвимость в Libreswan, позволяющая злоумышленнику восстановить предварительно заданный ключ IKEv1 при использовании агрессивного режима.