CVE-2016-3132 in PHP
Summary
by MITRE
Double free vulnerability in the SplDoublyLinkedList::offsetSet function in ext/spl/spl_dllist.c in PHP 7.x before 7.0.6 allows remote attackers to execute arbitrary code via a crafted index.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 09/12/2022
The CVE-2016-3132 vulnerability represents a critical double free error within PHP's SPL (Standard PHP Library) extension, specifically affecting the SplDoublyLinkedList::offsetSet function. This flaw exists in PHP versions 7.x prior to 7.0.6 and demonstrates how memory management issues in core language components can lead to remote code execution. The vulnerability arises from improper handling of memory allocation and deallocation when processing doubly linked list operations, creating conditions where the same memory block can be freed twice during the offsetSet operation. Such double free conditions are particularly dangerous because they can be exploited to manipulate heap memory layout and potentially redirect program execution flow.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious index value that triggers the double free scenario within the spl_dllist.c source file. When PHP processes a SplDoublyLinkedList::offsetSet call with specially crafted parameters, the underlying memory management code fails to properly track allocated memory blocks, resulting in the same memory address being freed twice. This memory corruption can be leveraged by attackers to overwrite critical data structures or function pointers, ultimately enabling arbitrary code execution on the target system. The vulnerability is particularly severe because it operates at the memory management level, bypassing many traditional security controls and operating within the PHP interpreter's core execution environment.
From an operational perspective, this vulnerability presents significant risk to web applications running vulnerable PHP versions, as it allows remote attackers to execute arbitrary code without requiring authentication or specific user interaction. The exploitability is enhanced by the fact that the vulnerability can be triggered through standard PHP array access operations, making it accessible through common web application attack vectors such as parameter injection, file upload handlers, or API endpoints that process user-supplied data. Organizations using PHP-based web applications are particularly vulnerable since the attack surface includes any application that utilizes SplDoublyLinkedList objects or similar data structures, potentially affecting thousands of websites and applications across various industries.
The vulnerability aligns with CWE-415, which describes double free conditions in memory management, and demonstrates characteristics that map to several ATT&CK techniques including T1059 for command and scripting interpreter usage, as well as T1078 for valid accounts and T1566 for credential access through exploitation of software vulnerabilities. Mitigation strategies should prioritize immediate patching of affected PHP installations to version 7.0.6 or later, where the double free issue has been resolved through proper memory management implementation. Additional defensive measures include implementing strict input validation for all user-supplied data, deploying web application firewalls to detect and block suspicious parameter patterns, and monitoring system logs for unusual memory allocation patterns that might indicate exploitation attempts. Organizations should also consider implementing runtime protections such as heap randomization and address space layout randomization to increase the difficulty of successful exploitation, though these measures provide only partial protection against such fundamental memory corruption vulnerabilities.