OAuth2 Token Validation Bypass in Open-Xchange

Executive Summary

This vulnerability involves OAuth2 token validation where an attacker with a token granting only part of the required scopes can authenticate successfully. The issue occurs because remote token validation accepts tokens with just one scope, while local validation correctly requires all scopes. This bypasses the intended authorization policy.

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Detection Guidance

Detecting this vulnerability requires checking if your OAuth2 token validation is using remote validation instead of local validation. Review your OAuth2 configuration files for token validation settings. Look for misconfigured authorization policies where tokens with partial scopes are accepted despite requiring multiple scopes.

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Impact Analysis

An attacker could gain unauthorized access to systems or data by exploiting this flaw. They might perform actions or access resources they shouldn't have permission for, leading to potential data breaches or misuse of services.

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Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating compliance requirements like GDPR or HIPAA. It may result in data breaches, unauthorized processing, or disclosure of protected information, triggering legal and regulatory penalties.

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Mitigation Strategies

Immediately switch to local token validation where tokens can be validated locally. Update to a non-vulnerable version of the software. Ensure your OAuth2 configuration enforces all required scopes and reject tokens with insufficient permissions.

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