CVE-2017-18239 in authentikat-jwt
Summary
by MITRE
A time-sensitive equality check on the JWT signature in the JsonWebToken.validate method in main/scala/authentikat/jwt/JsonWebToken.scala in authentikat-jwt (aka com.jason-goodwin/authentikat-jwt) version 0.4.5 and earlier allows the supplier of a JWT token to guess bit after bit of the signature by repeating validation requests.
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Analysis
by VulDB Data Team • 02/22/2023
This vulnerability exists in the authentikat-jwt library version 0.4.5 and earlier, where the JsonWebToken.validate method implements a time-sensitive equality check on JWT signatures. The flaw stems from an insecure comparison algorithm that introduces timing variations during signature validation, allowing attackers to perform bit-by-bit guessing of the signature through repeated validation requests. This timing-based side-channel attack exploits the differential execution time required for signature verification, where each failed comparison takes slightly longer than a successful one due to early termination conditions in the comparison logic. The vulnerability falls under CWE-208, which specifically addresses timing side channels, and represents a classic example of how seemingly innocuous cryptographic operations can introduce security weaknesses through implementation flaws rather than fundamental algorithmic issues.
The operational impact of this vulnerability is significant as it enables attackers to systematically brute-force JWT signatures through repeated validation attempts, potentially leading to unauthorized access to protected resources. An attacker can leverage this weakness by sending multiple JWT tokens with varying signature components and measuring response times to deduce the correct signature bits. This approach effectively transforms a computationally infeasible cryptographic attack into a practical timing-based exploitation technique that can be automated and executed within reasonable timeframes. The vulnerability particularly affects applications that rely on JWT-based authentication and authorization mechanisms, potentially compromising user sessions, access controls, and sensitive data protection.
Mitigation strategies should focus on implementing constant-time comparison algorithms for signature validation, ensuring that all comparisons take the same amount of time regardless of input values. This approach aligns with the security principle of constant-time execution and directly addresses the underlying timing side-channel vulnerability. Organizations should upgrade to patched versions of the authentikat-jwt library where the comparison logic has been replaced with secure constant-time implementations. Additionally, implementing rate limiting and request monitoring can help detect and prevent abuse of this vulnerability through automated attack patterns. The ATT&CK framework categorizes this as a timing side-channel attack technique, emphasizing the need for defensive measures that eliminate timing variations in cryptographic operations and maintain consistent execution patterns to prevent information leakage through temporal analysis.