CVE-2016-7133 in PHP
Summary
by MITRE
Zend/zend_alloc.c in PHP 7.x before 7.0.10, when open_basedir is enabled, mishandles huge realloc operations, which allows remote attackers to cause a denial of service (integer overflow) or possibly have unspecified other impact via a long pathname.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability identified as CVE-2016-7133 represents a critical security flaw in PHP 7.x versions prior to 7.0.10 that specifically affects systems utilizing the open_basedir configuration directive. This issue resides within the zend_alloc.c file, which serves as the core memory allocation module for PHP's Zend Engine. The vulnerability manifests when the open_basedir feature is enabled, creating a scenario where the system processes memory reallocation operations with excessively large parameters, leading to potential system instability and denial of service conditions. The flaw stems from improper handling of memory management operations that occur during the reallocation process, particularly when dealing with pathnames of considerable length.
The technical implementation of this vulnerability involves an integer overflow condition that occurs during memory reallocation operations. When PHP processes a pathname that exceeds normal operational limits while open_basedir is active, the system attempts to reallocate memory blocks using calculations that can exceed the maximum representable integer values. This overflow condition creates a scenario where the system allocates insufficient memory or incorrectly calculates memory requirements, resulting in memory corruption or allocation failures. The vulnerability specifically impacts the zend_mm_heap_realloc function which handles memory reallocation within PHP's memory manager. The flaw can be exploited by remote attackers who craft malicious pathnames that trigger the overflow condition during normal PHP processing operations.
The operational impact of CVE-2016-7133 extends beyond simple denial of service to potentially encompass arbitrary code execution or data corruption scenarios. The integer overflow creates conditions where attackers can manipulate memory allocation patterns to cause system crashes, memory corruption, or potentially execute malicious code within the PHP process context. When the system attempts to reallocate memory blocks with oversized parameters, it can lead to heap corruption that might be exploitable under certain conditions. The vulnerability is particularly concerning in web server environments where PHP processes user-supplied data, as attackers can craft malicious requests that trigger the overflow condition. This vulnerability affects the fundamental memory management capabilities of PHP, potentially compromising the entire application stack that relies on proper memory allocation behavior.
Mitigation strategies for CVE-2016-7133 focus primarily on updating PHP installations to versions 7.0.10 or later where the memory allocation handling has been corrected. System administrators should immediately apply the official PHP security patches that address the integer overflow condition in the zend_mm_heap_realloc function. Additionally, organizations should consider implementing input validation measures to limit pathname lengths and prevent exploitation attempts, though this represents a partial mitigation rather than a complete solution. The vulnerability aligns with CWE-190, Integer Overflow or Wraparound, which classifies this as a fundamental memory management flaw that can lead to various security consequences. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, Network Denial of Service, and potentially T1059.007, Command and Scripting Interpreter, when exploited for code execution. Organizations should also consider implementing network-based intrusion detection systems to monitor for exploitation attempts targeting this specific vulnerability pattern. The fix implemented in PHP 7.0.10 specifically addresses the memory allocation logic to prevent integer overflow conditions during reallocation operations, ensuring proper bounds checking and memory management throughout the allocation process.