Fix: prevent open redirect via returnTo in auth flow#22
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ralyodio merged 1 commit intoJun 15, 2026
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The returnTo parameter from the query string is stored in a cookie and used as the redirect target after OAuth callback. An attacker can set returnTo to an absolute URL (e.g. https://evil.com) to redirect users to a malicious site after login. Validate returnTo in both the auth initiation and callback routes to ensure it starts with / and is not a protocol-relative URL (//). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
Fixes #21
The
returnToparameter accepts arbitrary URLs, allowing an attacker to redirect users to external sites after OAuth login.Changes
apps/web/app/api/auth/coinpay/route.ts: ValidatereturnToat auth initiationapps/web/app/api/auth/callback/route.ts: ValidatereturnToat callback (defense-in-depth)Both checks ensure
returnTostarts with/and is not a protocol-relative URL (//).Test plan
returnTo=/dashboard— redirects to /dashboard after authreturnTo=https://evil.com— redirects to / insteadreturnTo=//evil.com— redirects to / instead🤖 Generated with Claude Code