CVE-2008-2108 in PHP
Summary
by MITRE
The GENERATE_SEED macro in PHP 4.x before 4.4.8 and 5.x before 5.2.5, when running on 64-bit systems, performs a multiplication that generates a portion of zero bits during conversion due to insufficient precision, which produces 24 bits of entropy and simplifies brute force attacks against protection mechanisms that use the rand and mt_rand functions.
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Analysis
by VulDB Data Team • 08/12/2019
The vulnerability described in CVE-2008-2108 represents a critical cryptographic weakness in PHP's random number generation mechanisms that affects versions prior to 4.4.8 and 5.2.5 when operating on 64-bit architectures. This flaw specifically targets the GENERATE_SEED macro implementation which is responsible for creating initial seed values for the rand and mt_rand functions. The issue manifests through insufficient precision during arithmetic operations on 64-bit systems, causing the multiplication process to produce portions of zero bits that significantly reduce the entropy of generated random sequences.
The technical root cause of this vulnerability lies in the improper handling of integer precision during the seed generation process on 64-bit platforms. When PHP executes the GENERATE_SEED macro on these systems, the multiplication operation fails to maintain adequate precision levels, resulting in the loss of significant bits during the conversion process. This computational artifact produces only 24 bits of effective entropy instead of the expected cryptographic strength, making the random number sequences predictable and vulnerable to brute force attacks. The vulnerability is particularly concerning because it affects fundamental cryptographic functions that many applications rely upon for security-sensitive operations.
The operational impact of this vulnerability extends beyond simple predictability issues, as it fundamentally undermines the security of applications that depend on PHP's random number generation for protection mechanisms. Attackers can exploit this weakness to reverse-engineer random sequences used in session management, password generation, token creation, and other security-critical functions. This weakness directly maps to CWE-330, which addresses insufficient entropy in random number generation, and aligns with ATT&CK technique T1112 for the exploitation of weak random number generators. The reduced entropy from 24 bits makes brute force attacks computationally feasible, potentially allowing adversaries to compromise session tokens, predict password resets, or bypass authentication mechanisms that rely on these flawed random number generators.
Mitigation strategies for this vulnerability require immediate patching of affected PHP installations to versions 4.4.8 and 5.2.5 or later, which contain the corrected GENERATE_SEED implementation. Organizations should also implement additional security controls such as monitoring for unusual patterns in random number usage and ensuring that critical security functions do not rely solely on the standard rand functions. System administrators should conduct comprehensive vulnerability assessments to identify applications that may be using affected PHP versions and prioritize remediation efforts based on the criticality of affected systems. The fix addresses the core precision issue in the multiplication process while maintaining compatibility with existing applications that depend on PHP's random number generation capabilities.