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Application & OT Security · Advanced

Host Header Injection

Abuse of an application's trust in the HTTP Host header to poison links, caches or routing.

Definition

Applications that build absolute URLs (for example password reset links) from the Host header can be tricked into sending links to attacker domains. Mitigations include configuring a fixed server name, validating Host against an allowlist and not using the header to build security-sensitive URLs.

Example

A password reset email contains a link to the attacker's domain because the app used the request's Host header.

Exam tip

Fix by hard-coding or allowlisting the canonical host.

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