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Application & OT Security · Advanced

DNS Rebinding

A technique in which a domain's DNS answer changes between validation and use, so a host check passes but the request goes to an internal IP.

Definition

Rebinding defeats SSRF filters that check the hostname's IP and then resolve again when connecting, and it can let malicious web pages reach devices on a victim's LAN. Mitigations include pinning the resolved IP for the request, validating Host headers on internal services and requiring authentication on local services.

Example

A filter resolves attacker.example to a public IP, but the HTTP client resolves it again to 169.254.169.254.

Exam tip

Resolve once, validate, and connect to that same IP.

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