JWT Scope and Audience Flaws Leave Go Microservices Open to Privilege Escalation

A technical analysis highlights how most Go microservice deployments correctly verify JWT signatures but fail on authorization semantics, creating exploitable security gaps. Two key failure modes are identified: scope inflation, where a broad token claim is accepted by unintended services, and audience misrouting, where tokens issued for one service are accepted by another due to skipped or misconfigured audience validation. The widely used golang-jwt/jwt library makes audience validation opt-in rather than enforced by default, meaning developers under deadline pressure often omit it entirely. This oversight can allow tokens meant for one service, such as a payments API, to be replayed against unrelated services like reporting, with no trace in logs. The article provides corrected Go code that enforces both audience and scope checks, arguing that without a coherent boundary contract, RBAC enforcement scattered across individual services creates privilege escalation paths that are nearly impossible to audit.