CVE-2022-31093 is a vulnerability in NextAuth.js, an open-source authentication library widely used in Next.js applications to manage user authentication flows. The flaw arises from improper handling of exceptional conditions during URL parsing of the `callbackUrl` query parameter. Specifically, when an attacker sends a request with a malformed `callbackUrl`, the NextAuth.js code attempts to instantiate a JavaScript URL object with this invalid string. This instantiation throws an unhandled exception because the URL constructor cannot process malformed URLs. The unhandled error causes the API route handler responsible for authentication to time out, resulting in failed login attempts. This denial-of-service-like behavior disrupts the authentication process, potentially locking out legitimate users. The vulnerability affects NextAuth.js versions prior to 3.29.5 and versions from 4.0.0 up to but not including 4.5.0. The issue has been addressed in versions 3.29.5 and 4.5.0 by implementing proper validation and error handling for the `callbackUrl` parameter. For environments where upgrading is not immediately feasible, the vendor recommends using Advanced Initialization techniques as a workaround to mitigate the issue. No known exploits have been reported in the wild, but the vulnerability poses a risk of service disruption through malformed URL inputs. The root cause is classified under CWE-754, indicating improper checks for unusual or exceptional conditions, which in this case leads to unhandled exceptions and service degradation.

For European organizations, the impact of this vulnerability primarily manifests as a denial-of-service condition affecting authentication services in web applications built with Next.js and using NextAuth.js for user login flows. Disruption of authentication can prevent legitimate users from accessing critical internal or customer-facing applications, potentially halting business operations or degrading user experience. This is particularly significant for sectors relying heavily on web portals for service delivery, such as finance, healthcare, e-commerce, and government services. Although the vulnerability does not directly lead to data leakage or privilege escalation, the inability to authenticate users can indirectly impact confidentiality and integrity by forcing fallback mechanisms or manual interventions. Additionally, repeated exploitation attempts could generate noise in logs and monitoring systems, complicating incident response. The lack of requirement for authentication or user interaction to trigger the issue means that attackers can remotely cause service outages without prior access, increasing the threat surface. However, since no active exploitation has been observed, the immediate risk is moderate but warrants timely remediation to prevent potential abuse.

European organizations should prioritize upgrading NextAuth.js to version 3.29.5 or later, or 4.5.0 or later, depending on their current major version, to ensure the vulnerability is fully patched. If upgrading is not immediately possible, implement the recommended Advanced Initialization workaround as documented by the NextAuth.js maintainers to handle malformed `callbackUrl` parameters safely. Additionally, organizations should implement input validation and sanitization at the application layer to reject or sanitize malformed URLs before they reach the authentication handler. Employing Web Application Firewalls (WAFs) with custom rules to detect and block requests containing suspicious or malformed URL parameters can provide a protective layer. Monitoring authentication API endpoints for unusual error rates or timeouts can help detect exploitation attempts early. Logging should be enhanced to capture malformed URL inputs triggering errors, aiding in forensic analysis. Finally, organizations should review their incident response plans to include scenarios involving authentication service disruption and ensure backup authentication mechanisms or failover procedures are in place to maintain business continuity.