CVE-2017-5340 in PHP
Summary
by MITRE
Zend/zend_hash.c in PHP before 7.0.15 and 7.1.x before 7.1.1 mishandles certain cases that require large array allocations, which allows remote attackers to execute arbitrary code or cause a denial of service (integer overflow, uninitialized memory access, and use of arbitrary destructor function pointers) via crafted serialized data.
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Analysis
by VulDB Data Team • 10/28/2022
The vulnerability identified as CVE-2017-5340 represents a critical security flaw within the PHP runtime environment that affects versions prior to 7.0.15 and 7.1.1. This issue resides in the zend_hash.c file which is responsible for managing hash tables and array operations within PHP's internal engine. The vulnerability manifests when PHP processes crafted serialized data that triggers specific conditions requiring large array allocations, creating a complex attack surface that can be exploited by remote adversaries.
The technical implementation of this vulnerability involves multiple interconnected flaws that compound the security risk. The primary issue stems from integer overflow conditions that occur during array allocation calculations, allowing attackers to manipulate memory allocation parameters beyond normal limits. Additionally, the flaw enables uninitialized memory access patterns where PHP attempts to read from memory locations that have not been properly initialized, creating potential information disclosure and code execution opportunities. The most concerning aspect involves the use of arbitrary destructor function pointers, which allows attackers to redirect execution flow to malicious code through carefully crafted serialized data structures that specify custom cleanup functions.
This vulnerability operates under the broader context of PHP's serialization mechanism and its handling of complex data structures. When PHP encounters serialized data containing arrays with specific characteristics, the zend_hash.c implementation fails to properly validate allocation requirements, leading to memory corruption that can be exploited for remote code execution. The attack vector typically involves sending malicious serialized data to a PHP application that processes the data through functions like unserialize(), creating a path for arbitrary code execution or denial of service conditions. The integer overflow specifically occurs when calculating array sizes that exceed the maximum representable value for the underlying integer type, causing unexpected behavior in memory allocation routines.
The operational impact of CVE-2017-5340 extends beyond simple denial of service scenarios to encompass full remote code execution capabilities. Attackers can leverage this vulnerability to execute arbitrary commands on vulnerable systems, potentially leading to complete system compromise. The vulnerability affects web applications that utilize PHP's serialization features, making it particularly dangerous in environments where user input is processed through unserialize() functions without proper validation. This flaw aligns with CWE-190, which addresses integer overflow conditions, and CWE-476, which covers null pointer dereferences that can occur in memory management operations. The vulnerability also maps to ATT&CK technique T1059.007 for remote code execution through PHP applications and T1499.004 for denial of service attacks targeting application availability.
Mitigation strategies for this vulnerability require immediate patching of affected PHP installations to versions 7.0.15 or later and 7.1.1 or later, which contain the necessary fixes for the integer overflow and memory management issues. Organizations should also implement proper input validation and sanitization for all serialized data, particularly when processing user-provided content through unserialize() functions. Additional defensive measures include restricting the use of unserialize() with untrusted data, implementing proper access controls for PHP applications, and monitoring application logs for suspicious serialization patterns. Security teams should also consider implementing application firewalls and intrusion detection systems to monitor for exploitation attempts targeting this specific vulnerability class. The fix addresses the underlying memory management issues by properly validating array allocation sizes and ensuring that destructor function pointers are properly validated before execution, preventing the arbitrary code execution pathways that previously existed in vulnerable configurations.