JWT Algorithm Confusion to Account Takeover: RS256→HS256, JKU Injection & kid SQLi
JSON Web Tokens (JWTs) are the de facto authentication primitive across modern web applications, microservices, and APIs. Yet their flexibility, specifically the delegated algorithm selection embedded within each token, has repeatedly proven catastrophic. Six new critical CVEs affecting widely-deployed JWT libraries were disclosed in 2025 alone, with several enabling full