CVE-2024-25191 in php-jwt
Summary
by MITRE • 02/08/2024
php-jwt 1.0.0 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 • 06/12/2025
The vulnerability identified as CVE-2024-25191 affects the php-jwt library version 1.0.0 and represents a critical security flaw that undermines the integrity of authentication mechanisms through timing side channel attacks. This issue stems from the library's implementation of authentication verification using the standard strcmp function, which does not provide constant-time execution behavior. The vulnerability exposes the system to sophisticated attacks that exploit timing differences in string comparison operations to infer sensitive information about authentication tokens.
The technical flaw manifests in the library's handling of JWT token verification where the strcmp function is employed to compare expected and actual token values. Unlike constant-time comparison functions such as hash_equals or timing-safe string comparison routines, strcmp executes with variable timing based on the position of the first mismatched character. This timing variation creates a measurable side channel that attackers can exploit to perform brute force attacks against authentication tokens. The vulnerability falls under the category of timing side channel attacks as defined by the CWE-398 weakness classification, specifically CWE-398: Indicator of Poor Code Quality, which encompasses code that is vulnerable to timing attacks due to non-constant time operations.
The operational impact of this vulnerability extends beyond simple authentication bypass to potentially compromise entire systems that rely on JWT-based authentication mechanisms. Attackers can systematically determine valid authentication tokens by measuring response times during token verification processes, effectively reducing the search space for valid tokens from exponential to linear complexity. This makes the vulnerability particularly dangerous in environments where JWT tokens are used for session management, API authentication, or access control. The attack vector aligns with the MITRE ATT&CK framework under the technique T1212: Exploitation for Credential Access, where adversaries leverage timing side channels to obtain valid credentials or access tokens.
Security professionals should immediately assess their systems for dependency on the vulnerable php-jwt 1.0.0 library and implement comprehensive mitigation strategies. The primary remediation involves upgrading to a patched version of the library that employs constant-time string comparison functions such as hash_equals or equivalent timing-safe operations. Organizations must also conduct thorough security assessments of all applications that utilize JWT authentication to identify potential exposure to similar timing vulnerabilities. Additionally, implementing proper input validation, rate limiting, and monitoring for unusual authentication patterns can help detect and prevent exploitation attempts. The vulnerability demonstrates the critical importance of constant-time operations in cryptographic implementations and highlights the necessity of adhering to established security best practices for authentication mechanisms.