Fix redirect target comes from the caller in Astro

The destination of a redirect is taken from the request without being checked. An attacker can send a link that starts with your domain and ends on theirs, which is what makes a phishing page credible - and in an OAuth callback it hands the authorisation code to whoever asked. Resolve the target against your own origin and refuse anything else.

medium likely Astro CWE-601 / OWASP A01:2021

The vulnerable pattern in Astro

MEDIUM likely Redirect target comes from the caller A01:2021 src/pages/api/proxy.ts:55:12 53 │ // open-redirect: Astro's redirect() to a caller-chosen target. 54 │ if (next) { 55 │ return redirect(next) │ ~~~~~~~~~~~~~~ destination chosen by the caller 56 │ }

This finding comes from the Astro fixture in the owlwarden test suite, in /api/proxy. The whole redirect target comes from the request, so a link to this endpoint can send a visitor anywhere. The URL they click genuinely belongs to you, which is what makes the page they land on convincing - and on an OAuth callback the authorisation code goes with them.

The corrected handler

Validate before calling redirect(); the request URL's origin is the base.

export async function GET({ request, redirect }: APIContext) {
  const next = new URL(request.url).searchParams.get('next')
  return redirect(safeRedirect(next, new URL(request.url).origin))
}

If you are not using Astro

Resolve the target against your own origin and refuse anything that lands elsewhere. Do not use a startsWith('/') check: '//evil.com' passes it and leaves the site.

Check your own repository

npx owlwarden scan
npx owlwarden explain open-redirect

Runs on your machine. No account, no telemetry, no network unless you ask. In CI, SARIF uploads to code scanning and the exit code is the gate.

Other Astro checks

Rules with a tested Astro example.

open-redirect for every framework / All rules / owlwarden