CVE-2007-4661 in PHP
Summary
by MITRE
The chunk_split function in string.c in PHP 5.2.3 does not properly calculate the needed buffer size due to precision loss when performing integer arithmetic with floating point numbers, which has unknown attack vectors and impact, possibly resulting in a heap-based buffer overflow. NOTE: this is due to an incomplete fix for CVE-2007-2872.
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Analysis
by VulDB Data Team • 07/25/2019
The chunk_split function in PHP 5.2.3 contains a critical buffer overflow vulnerability stemming from improper integer arithmetic handling during buffer size calculation. This flaw represents a regression issue that emerged from an incomplete remediation of CVE-2007-2872, demonstrating how security fixes can sometimes introduce new vulnerabilities through inadequate testing or understanding of underlying mathematical operations. The vulnerability manifests when PHP processes strings through the chunk_split function, which is commonly used for formatting text output in web applications.
The technical root cause involves precision loss during integer arithmetic operations that utilize floating point numbers for buffer size calculations. When PHP's chunk_split function processes input strings, it performs mathematical operations to determine the required buffer space for the output. However, the implementation fails to maintain sufficient precision during these calculations, leading to incorrect buffer size determinations. This precision loss occurs at the intersection of integer and floating point arithmetic operations, where the conversion process introduces rounding errors that compound during subsequent calculations. The vulnerability specifically affects the string.c file in PHP's core library, making it a fundamental issue within the language's runtime environment.
The operational impact of this vulnerability extends beyond simple buffer overflow conditions to potentially enable arbitrary code execution within the context of the web server process. Attackers could exploit this weakness by crafting malicious input strings that, when processed through chunk_split, cause the application to allocate insufficient buffer space. This misallocation creates heap corruption conditions that may allow attackers to overwrite adjacent memory locations, potentially leading to privilege escalation or remote code execution. The unknown attack vectors and impact classification indicate that the full scope of exploitation methods remains unclear, but the heap-based nature of the vulnerability suggests it could be leveraged through various input manipulation techniques. The vulnerability's severity is compounded by its potential to affect numerous web applications that rely on PHP's string processing capabilities.
Mitigation strategies for this vulnerability require immediate patching of affected PHP installations to the latest stable versions that contain proper fixes for both CVE-2007-4661 and its predecessor CVE-2007-2872. Organizations should implement input validation measures that limit the size and complexity of strings processed through chunk_split operations, particularly when handling user-supplied data. Additionally, deploying web application firewalls and implementing proper memory protection mechanisms can help detect and prevent exploitation attempts. The vulnerability aligns with CWE-129, which addresses improper validation of array indices, and may map to ATT&CK techniques involving code injection and privilege escalation. System administrators should also consider implementing runtime monitoring to detect anomalous memory allocation patterns that could indicate exploitation attempts. Regular security audits and vulnerability assessments should include checks for similar arithmetic precision issues in other mathematical operations within the PHP runtime environment.