Why JWT token inspection should run entirely client-side to mitigate CVE-2026-118759
A recently disclosed vulnerability, CVE-2026-118759, involves authentication token leakage and session fixation tied to insecure loopback cookies. Attackers can exploit man-in-the-middle interception when developers paste live production tokens into centralized online formatters. Traditional SaaS formatters may record input headers, session IDs, and user metadata in access logs, exposing secrets. The article recommends verifying tokens entirely in the browser using the standard WebCrypto API so that credentials never leave the local machine. It includes a sample RSA signature verification function and points to RFC 7519 and the W3C Web Cryptography API as reference standards.
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