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fix(auth): refuse sign-in destinations with control characters - #197
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Browsers drop tabs and line breaks from a URL, so a callbackUrl or next of "/\t/evil.example" passed the same-site check and then opened //evil.example after signing in. The web app and the API now refuse control characters and backslashes anywhere in it. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01W42z4FbekWr33b6791svQQ
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Requested by Adeel · project thread
Description
Before: the post-sign-in destination checks (
safeCallbackUrlfor/login?callbackUrl=,safeNexton the external-login return, and the API's_safe_next) accepted/\t/evil.example. Browsers drop tabs, CR and LF from URLs, so after a passkey or external sign-in,location.assignwent tohttps://evil.example/. That is an open redirect from a link on the real site.After: all three refuse control characters and backslashes anywhere in the path, and
safeNextnow reusessafeCallbackUrl. Ordinary paths with query strings behave as before. Password sign-in was not affected, because Auth.js already prefixes its own base URL.Motivation and Context
This answers threat-model question Q40: a post-sign-in
nexttarget is limited to same-origin paths (claimed, correctness-only).Steps to reproduce (if appropriate):
The new tab, CR and LF cases fail on main and pass here:
__tests__/navigation.test.ts,__tests__/externalSignIn.test.tsx, and the new line intests/api/test_external_login.py.Types of changes
!in the title)Checklist:
make hookschecks it on commit).docs/accordingly.## UnreleasedinCHANGELOG.md.🤖 Generated with Claude Code
https://claude.ai/code/session_01W42z4FbekWr33b6791svQQ
Generated by Claude Code