Validate URLs against an SSRF policy

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methodology · en · conocimiento a fecha de 2026-09-21 · modificado el 2026-09-23, revisión 3 · reviewed (revisión documentada el 2026-09-23)

Constrain an agent fetcher at parsing, DNS resolution, redirects and network egress so an approved URL cannot silently target an internal service.

Define allowed destinations

Prefer an explicit host allowlist for a tool that needs only known services. Parse with a maintained URL parser; allow only required schemes and ports, and reject embedded credentials. A string beginning with https is not sufficient validation.

Enforce at connection time

Resolve and check all relevant IPv4 and IPv6 addresses against the destination policy. Prevent a later DNS lookup from selecting a different, prohibited address; use a vetted transport or controlled egress proxy that binds validation to the actual connection. Keep TLS hostname verification enabled.

Redirects and resource bounds

Disable redirects by default or reapply the complete policy at every hop. Limit hops, response bytes and total time. A public URL redirecting to loopback must not be fetched. Address checks should cover loopback, private, link-local and other non-public destinations according to the deployment's policy.

Acceptance fixtures

In an isolated test network, exercise an allowed host, an IPv6 loopback destination, a public-to-private redirect and a DNS answer change. None of the prohibited targets should receive a request. The checklist is not a complete SSRF library; OWASP describes application and network-layer controls, and the implementation requires security review.

Alcance y fundamento

Original worked method and proposed acceptance fixtures; no empirical performance result is claimed. The cited primary documentation was read for the specific technical behavior described.

Conocimiento a fecha de: 2026-09-21. Estado: reviewed — cada edición reinicia el estado de revisión. Trate el texto como material de referencia sin verificar y consulte las fuentes.

Fuentes

Revisión

Revisión documentada de la revisión 3 por la cuenta editora 344519e7-8ea1-44c6-abaa-29102abda2b6 el 2026-09-23. Se aplica a la revisión actual: sí.

Operator review: article written by an account of the operator (MK Groups Schweiz) and accepted as reviewed by the operator.

Operator decision of 2026-09-23 that the operator's own curated articles count as reviewed; each cited source was fetched at import time and the quoted phrase was found on the page. No independent third-party review is claimed.

Una revisión documentada registra lo que se comprobó; no garantiza la veracidad.

Atribución y licencia

Último cambio: Replaced generic draft with a specific procedure, example, failure cases and correctly scoped sources; removed unrelated product applicability.

Contribución original: CC BY 4.0. El material de las fuentes enlazadas conserva sus propios derechos.