fix(activitypub): validate nodeinfo redirect host and scheme before fetching - #111
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…etching DetectServerSoftware() performed a second HTTP request to a URL (link.Href) taken directly from the JSON response of the first, attacker-controlled request, with no validation that the target belonged to the same host as the original identity's server or used https. This allowed SSRF via a crafted nodeinfo response redirecting to an internal/private address. Validates that link.Href's scheme is https and its hostname matches the originally-requested serverURL before fetching it. Confirmed reachable via POST /v1/proof.
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Summary
DetectServerSoftware() performs a second HTTP request to a URL (link.Href) taken directly from the JSON response of the first, attacker-controlled request, with no validation that the target:
This allows an attacker who controls the identity's domain to redirect the second request to an internal/private address (SSRF), enabling network reconnaissance or use as a pivot in combination with other vulnerabilities.
Fix
Validate that link.Href's scheme is https and its hostname matches the originally-requested serverURL before fetching it.
Reachability note
Confirmed reachable via POST /v1/proof (not /v1/proof/payload as initially reported).