CVE-2008-2107 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 32-bit systems, performs a multiplication using values that can produce a zero seed in rare circumstances, which allows context-dependent attackers to predict subsequent values of the rand and mt_rand functions and possibly bypass protection mechanisms that rely on an unknown initial seed.
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Analysis
by VulDB Data Team • 03/16/2021
The vulnerability described in CVE-2008-2107 represents a critical weakness in PHP's random number generation mechanism that affects versions prior to 4.4.8 and 5.2.5 when operating on 32-bit systems. This issue resides within the GENERATE_SEED macro implementation that is responsible for initializing the random number generators rand() and mt_rand() functions. The flaw manifests specifically in the multiplication operation used to generate the initial seed value, where certain input conditions can result in a zero seed being produced. This zero seed value fundamentally compromises the randomness of the subsequent number sequences generated by these functions, creating predictable patterns that can be exploited by malicious actors.
The technical implementation of this vulnerability stems from the mathematical operations performed within the seed generation process on 32-bit architectures. When the multiplication operation involving the seed values produces a result that equals zero, the random number generator loses its entropy and becomes deterministic. This occurs because the rand() and mt_rand() functions rely on the initial seed to establish their internal state, and when that seed becomes zero, the entire sequence becomes predictable. The vulnerability is particularly concerning because it operates in rare circumstances, making it difficult to detect during normal operation but exploitable when the specific mathematical conditions are met. This characteristic aligns with CWE-330 Use of Insufficiently Random Values, which specifically addresses weaknesses in cryptographic and pseudo-random number generation where insufficient entropy leads to predictable outputs.
The operational impact of this vulnerability extends beyond simple predictability issues and can severely compromise security systems that depend on random number generation for protection mechanisms. Attackers can exploit this weakness to predict future values of the random number generators, potentially allowing them to bypass security controls that rely on unpredictable values such as session identifiers, cryptographic keys, or nonce values. The context-dependent nature of the attack means that an attacker must understand the specific conditions under which the zero seed occurs, but once achieved, the predictability can be used to compromise authentication systems, session management, and other security-critical functions. This vulnerability directly relates to ATT&CK technique T1112, which covers the exploitation of weaknesses in random number generation to predict system behavior and compromise security controls. The attack surface is particularly broad because many applications depend on PHP's random number functions for various security operations, making this vulnerability potentially exploitable across multiple attack vectors.
Mitigation strategies for CVE-2008-2107 focus primarily on upgrading PHP installations to versions that contain the patched implementations of the GENERATE_SEED macro. Organizations should immediately upgrade to PHP 4.4.8 or PHP 5.2.5 and later versions where the seed generation algorithm has been corrected to prevent zero seed occurrences. Additionally, system administrators should implement monitoring to detect any unusual patterns in random number generation that might indicate exploitation attempts. For systems where immediate upgrades are not feasible, developers can implement additional entropy sources or alternative random number generation methods to supplement the vulnerable PHP functions. Security teams should also review applications that rely heavily on PHP's random number generation for session management, authentication tokens, or cryptographic operations to ensure that the vulnerability has been properly addressed. The remediation process should include thorough testing to verify that the fixed implementations produce sufficiently random values and that no regression issues have been introduced in the application functionality.