CVE-2016-7037 in JWT
Summary
by MITRE
The verify function in Encryption/Symmetric.php in Malcolm Fell jwt before 1.0.3 does not use a timing-safe function for hash comparison, which allows attackers to spoof signatures via a timing attack.
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Analysis
by VulDB Data Team • 11/18/2025
The vulnerability identified as CVE-2016-7037 resides within the jwt library developed by Malcolm Fell, specifically in the Encryption/Symmetric.php file. This issue affects versions prior to 1.0.3 and represents a critical security flaw that undermines the integrity of signature verification processes. The core problem lies in the implementation of the verify function which fails to employ timing-safe hash comparison mechanisms, creating a window of opportunity for malicious actors to exploit temporal variations in processing time.
The technical flaw manifests through the use of standard string comparison operations instead of constant-time algorithms for verifying cryptographic signatures. When an attacker can measure the time taken to process different signature attempts, they can deduce information about the correct signature through timing variations. This type of attack leverages side-channel information where the temporal behavior of the system reveals cryptographic secrets. The vulnerability directly relates to CWE-203, which describes "Observable Behavioral Vulnerability," and more specifically aligns with CWE-327, "Use of a Broken or Risky Cryptographic Algorithm," as it undermines the fundamental security assumptions of cryptographic verification.
The operational impact of this vulnerability extends beyond simple authentication bypasses, as it can enable complete signature spoofing attacks against systems relying on the affected jwt library. An attacker can systematically determine valid signatures by measuring response times, potentially leading to unauthorized access to protected resources, data manipulation, or complete system compromise. The timing attack approach allows for practical exploitation without requiring extensive computational resources, making it particularly dangerous in production environments where signature verification occurs frequently.
Mitigation strategies for CVE-2016-7037 require immediate upgrade to jwt library version 1.0.3 or later, which implements proper timing-safe hash comparison functions. Organizations should also consider implementing additional security measures such as rate limiting, monitoring for unusual timing patterns, and comprehensive code reviews to identify similar vulnerabilities in other cryptographic implementations. The remediation process must include thorough testing to ensure that the updated library functions correctly without introducing regressions in existing applications. Security teams should also consider implementing the ATT&CK framework's T1212 technique for detecting and preventing timing-based attacks, as this vulnerability represents a classic example of side-channel information leakage that can be systematically exploited by threat actors.