CVE-2008-4125 in phpBB
Summary
by MITRE
The search function in phpBB 2.x provides a search_id value that leaks the state of PHP s PRNG, which allows remote attackers to obtain potentially sensitive information, as demonstrated by a cross-application attack against WordPress, a different vulnerability than CVE-2006-0632.
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Analysis
by VulDB Data Team • 10/08/2018
The vulnerability described in CVE-2008-4125 represents a significant cryptographic weakness in phpBB 2.x forums that stems from improper handling of random number generation within the search functionality. This flaw exists in the search_id parameter generation process where the application inadvertently exposes the internal state of PHP's pseudo-random number generator through predictable output patterns. The vulnerability specifically affects versions of phpBB 2.x that utilize the default PHP random number generation mechanisms, creating a scenario where attackers can infer the state of the PRNG based on observed search_id values.
The technical exploitation of this vulnerability occurs when remote attackers can observe multiple search_id values generated by the phpBB application and use this information to reconstruct the internal state of the PHP PRNG. This reconstruction enables attackers to predict future random values that the application might generate, potentially allowing them to craft malicious requests or bypass security mechanisms that rely on random values for session management or access control. The vulnerability demonstrates a classic example of poor entropy management in cryptographic implementations, where predictable outputs from a pseudo-random number generator compromise the security of the entire system. This issue is particularly concerning because it operates at the application layer and can be exploited without requiring privileged access or deep system knowledge.
The operational impact of this vulnerability extends beyond the immediate phpBB installation to create cross-application attack vectors that can affect other systems within the same network infrastructure. As demonstrated in the CVE description, attackers can leverage this weakness to target WordPress installations or other applications that may share similar cryptographic vulnerabilities or dependencies. The attack surface expands significantly because the leaked PRNG state can be used to predict random values in systems that may be interconnected or share common infrastructure components. This cross-application nature makes the vulnerability particularly dangerous for organizations running multiple web applications that may be vulnerable to similar PRNG-related attacks. The vulnerability also aligns with ATT&CK technique T1083 (File and Directory Discovery) and T1112 (Modify Registry) when considering how attackers might use the leaked information to manipulate system behavior or predict security tokens.
Mitigation strategies for this vulnerability require immediate application of security patches provided by phpBB developers, as well as implementation of proper random number generation practices within the application. Organizations should ensure that all applications utilize cryptographically secure random number generators rather than relying on default PHP PRNG implementations for security-sensitive operations. The fix typically involves updating the phpBB installation to a patched version that properly handles random number generation within search functions, and implementing additional security controls such as rate limiting and input validation to prevent exploitation. Security teams should also conduct thorough audits of their application code to identify other potential uses of insecure random number generation and ensure compliance with industry standards such as those outlined in NIST SP 800-90A for cryptographic random number generation. The vulnerability serves as a reminder of the critical importance of proper entropy management in cryptographic implementations and the potential for seemingly minor flaws to create significant security risks across interconnected systems.
This vulnerability exemplifies CWE-330 (Use of Insufficiently Random Values) and demonstrates how weak random number generation can create cascading security issues that extend beyond the immediate affected component. The cross-application nature of the attack vector highlights the interconnectedness of modern web applications and the need for comprehensive security approaches that consider the entire attack surface rather than individual components in isolation. Organizations must implement robust security practices including regular vulnerability assessments, proper patch management, and adherence to established security frameworks to prevent exploitation of similar weaknesses in their infrastructure.