ADVISORIES

• CVE-2018-1000539 (NVD)
• GHSA-mj4x-wcxf-hm8x
• Vendor Advisory

GEM

json-jwt

SEVERITY

CVSS v3.x: 5.3 (Medium)

UNAFFECTED VERSIONS

• < 0.5.1

PATCHED VERSIONS

• >= 1.9.4

DESCRIPTION

Ruby’s OpenSSL bindings do not check the length of the supplied authentication tag when decrypting an authenticated encryption mode such as AES-GCM, leaving this up to the authors of a gem/app to implement for properly validating the message.

json-jwt was not checking for the authentication tag length, meaning that with a one byte tag the JWT would be considered not tampered with. This means that with an average of 128 (max 256) attempts an attacker can forge a valid signature.