CVE-2024-25189 in libjwt
Summary
by MITRE • 02/08/2024
libjwt 1.15.3 uses strcmp (which is not constant time) to verify authentication, which makes it easier to bypass authentication via a timing side channel.
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Analysis
by VulDB Data Team • 08/26/2024
The vulnerability identified as CVE-2024-25189 affects libjwt version 1.15.3 and represents a critical security flaw in the JSON Web Token library's authentication verification process. This issue stems from the library's use of the standard strcmp function for comparing authentication tokens, which creates a predictable timing side channel that attackers can exploit to bypass authentication mechanisms. The fundamental problem lies in how strcmp operates by comparing strings character by character until a mismatch is found, resulting in variable execution times that correlate directly with the position of the first differing character. This timing variation provides attackers with measurable information about the correct authentication data, enabling them to perform systematic brute force attacks with significantly reduced computational overhead compared to traditional approaches.
The technical implementation flaw resides in the library's cryptographic verification routines where constant-time string comparison functions should be employed instead of standard string comparison functions. This vulnerability directly maps to CWE-203, which specifically addresses the exposure of sensitive information through side channels, and more broadly to CWE-310, concerning cryptographic issues related to improper implementation of security functions. The timing side channel attack exploits the fact that strcmp returns immediately upon detecting a mismatch, meaning that the longer an attacker's guess remains correct up to a certain point, the more time the comparison takes to complete. This behavior creates a measurable timing difference that can be amplified through statistical analysis and repeated attempts to reconstruct the correct authentication token.
The operational impact of this vulnerability extends beyond simple authentication bypasses, as it undermines the fundamental security assumptions of any system relying on libjwt for token validation. Attackers can systematically determine valid tokens by measuring response times and identifying when their guesses match the correct values, potentially leading to unauthorized access to protected resources, privilege escalation, and data breaches. The vulnerability affects any application or service that depends on libjwt 1.15.3 for authentication, including web applications, API gateways, and microservices architectures that utilize JSON Web Tokens for session management and access control. This weakness is particularly dangerous in environments where authentication tokens are frequently validated, as the cumulative timing information can be used to reconstruct complete tokens through statistical analysis rather than brute force methods that would normally require exponential time complexity.
Mitigation strategies for CVE-2024-25189 should prioritize immediate patching of libjwt to version 1.15.4 or later, which includes proper constant-time string comparison implementations. Organizations should also implement monitoring systems to detect unusual timing patterns in authentication requests that could indicate side channel attacks. The recommended approach aligns with ATT&CK technique T1212, which focuses on exploitation of information disclosure vulnerabilities, and emphasizes the importance of using constant-time comparison functions such as memcmp or specialized cryptographic libraries that provide timing-attack resistant operations. Additionally, security teams should consider implementing rate limiting and account lockout mechanisms to further reduce the effectiveness of timing-based attacks while awaiting full patch deployment. The vulnerability serves as a reminder of the critical importance of constant-time operations in cryptographic implementations and the potential consequences of overlooking side channel considerations in security-sensitive code.