CVE-2001-1534 in HTTP Server
Summary
by MITRE
mod_usertrack in Apache 1.3.11 through 1.3.20 generates session ID s using predictable information including host IP address, system time and server process ID, which allows local users to obtain session ID s and bypass authentication when these session ID s are used for authentication.
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Analysis
by VulDB Data Team • 09/24/2025
The vulnerability identified as CVE-2001-1534 resides within the mod_usertrack module of Apache HTTP Server versions 1.3.11 through 1.3.20, representing a significant weakness in session management that directly impacts authentication security. This module was designed to track user sessions through cookies, but its implementation suffered from a fundamental flaw in randomness generation that made session identifiers highly predictable. The vulnerability falls under the category of weak cryptographic randomness as classified by CWE-330, where the predictable nature of generated session IDs creates a pathway for attackers to compromise authentication mechanisms.
The technical flaw stems from the mod_usertrack module's use of deterministic information sources when generating session identifiers. Specifically, the module incorporates host IP address, system time, and server process ID into the session ID generation algorithm, creating a predictable pattern that local users can exploit. This approach violates the fundamental security principle that session identifiers must be cryptographically secure and unpredictable to prevent session hijacking attacks. The combination of these three data points creates a relatively small entropy space that can be easily enumerated or guessed by an attacker with access to the local system, as the host IP address remains constant, system time can be estimated through network timing attacks, and process IDs follow predictable patterns.
The operational impact of this vulnerability extends beyond simple session tracking issues, as it enables local users to bypass authentication mechanisms entirely. When session IDs generated by mod_usertrack are used for authentication purposes, attackers can predict valid session identifiers and impersonate legitimate users. This creates a privilege escalation scenario where local users gain unauthorized access to protected resources, potentially leading to complete system compromise. The vulnerability is particularly dangerous in environments where local access is possible, as it eliminates the need for complex exploitation techniques. This weakness directly aligns with the ATT&CK technique T1548.003 - Abuse Elevation Control Mechanism, where attackers leverage predictable session identifiers to bypass authentication controls.
The security implications of this vulnerability are compounded by the fact that it affects a core web server module that was widely deployed in production environments. Organizations using Apache 1.3.x series servers with mod_usertrack enabled were exposed to this risk, as the predictable session ID generation created a persistent backdoor that could be exploited by anyone with local access to the system. The vulnerability also demonstrates poor security engineering practices in session management, where the use of non-random data sources for critical security functions represents a fundamental design flaw. Organizations should have implemented proper entropy sources and cryptographic random number generation to ensure session identifiers remained unpredictable. This vulnerability underscores the importance of following security best practices such as those outlined in NIST SP 800-90A for random number generation and highlights the critical need for regular security assessments of web server configurations to identify and remediate such weaknesses before they can be exploited by malicious actors.