Fix redirect target comes from the caller in Koa

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 Koa CWE-601 / OWASP A01:2021

The vulnerable pattern in Koa

MEDIUM likely Redirect target comes from the caller A01:2021 src/app.ts:58:3 56 │ // Pass the query read straight in - parking it behind `??` breaks the 57 │ // one-hop origin tracker (same shape as express-api). 58 │ ctx.redirect(ctx.query.next as string) │ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ destination chosen by the caller 59 │ })

This finding comes from the Koa fixture in the owlwarden test suite. 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 ctx.redirect().

const base = `${ctx.protocol}://${ctx.host}`
ctx.redirect(safeRedirect(ctx.query.next, base))

If you are not using Koa

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 Koa checks

Rules with a tested Koa example.

open-redirect for every framework / All rules / owlwarden