The vulnerability in nuts-node involves insufficient verification of data authenticity at the /auth/v1/introspect_access_token endpoint. Specifically, the endpoint accepts any JWT signed by a node key without validating critical aspects such as JWT type, issuer-to-key binding, and required claims. This enables an attacker to replay a Verifiable Presentation JWT as an access token, causing the system to incorrectly mark it as active. The vulnerability affects nuts-node versions >= 6.0.0-alpha.1 and < 6.2.3, and versions below 5.4.31. The issue is addressed by fixes in versions 6.2.3 and 5.4.31.

An attacker can replay a Verifiable Presentation JWT as an access token, causing the introspection endpoint to return an active: true response. This may lead to unauthorized access or privilege escalation within systems relying on this token introspection. The CVSS score of 4.4 reflects a medium severity with network attack vector, high attack complexity, low privileges required, and user interaction needed. Confidentiality and integrity impacts are low, with no availability impact.

This vulnerability is fixed in nuts-node versions 6.2.3 and 5.4.31. Users should upgrade to these or later versions to remediate the issue. Patch status is not explicitly stated as 'official-fix' in the vendor advisory, but the description confirms the fix is included in these versions. No additional mitigation steps are indicated.