Severity: high

    Signature Verification Bypass



    Versions of jwt-simple prior to 0.5.3 are vulnerable to Signature Verification Bypass. If no algorithm is specified in the decode() function, the packages uses the algorithm in the JWT to decode tokens. This allows an attacker to create a HS256 (symmetric algorithm) JWT with the server's public key as secret, and the package will verify it as HS256 instead of RS256 (asymmetric algorithm).


    Upgrade to version 0.5.3 or later.

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    Advisory timeline

    1. published

      Advisory Published
      Apr 24th, 2019
    2. reported

      Reported by Daniel Gunawan
      Apr 24th, 2019