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The vulnerability in the Auth0 Next.js SDK involves improper input validation of the returnTo parameter during OAuth authentication flows. In affected versions, the SDK fails to sanitize user-controlled input in the returnTo parameter when constructing authorization requests to Auth0. Attackers can craft URLs with malicious returnTo values that include additional OAuth query parameters, such as scope or audience. When a user clicks on such a link and initiates login, the SDK incorporates the injected parameters into the Auth0 authorization request. The Auth0 server processes these parameters as part of the OAuth request, potentially issuing tokens with unintended scopes or audiences. This allows attackers to manipulate token claims, leading to privilege escalation or unauthorized access. The flaw exists in functions like handleLogin and handleCallback, where the returnTo parameter is used without strict validation. Exploitation requires social engineering to lure users to malicious login links. Upon authentication, the compromised tokens reflect the injected parameters, enabling further attacks. The vulnerability is mitigated in version 4.13.0 through proper validation and sanitization of the returnTo parameter.
Platform: Auth0 Next.js SDK
Version: 4.9.0-4.12.0
Vulnerability: Query Parameter Injection
Severity: Low
Date: 2025-12-10
Prediction: Patched v4.13.0
What Undercode Say:
Analytics:
- Check version: `npm list @auth0/nextjs-auth0`
– Scan package.json: `grep \”@auth0/nextjs-auth0\” package.json`
– Upgrade command: `npm install @auth0/[email protected]`
Exploit:
- Craft malicious returnTo URL.
- Inject OAuth query parameters.
- Trick user into clicking.
Protection:
- Upgrade to v4.13.0.
- Sanitize returnTo parameter.
- Validate user input.
Impact:
- Unintended token parameters.
- Privilege escalation possible.
- Data exposure risk.
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Sources:
Reported By: github.com
Extra Source Hub:
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