CVE-2015-4116 in PHP
Summary
by MITRE
Use-after-free vulnerability in the spl_ptr_heap_insert function in ext/spl/spl_heap.c in PHP before 5.5.27 and 5.6.x before 5.6.11 allows remote attackers to execute arbitrary code by triggering a failed SplMinHeap::compare operation.
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Analysis
by VulDB Data Team • 08/19/2022
The CVE-2015-4116 vulnerability represents a critical use-after-free flaw in PHP's Standard PHP Library implementation that affects versions prior to 5.5.27 and 5.6.11. This vulnerability exists within the spl_ptr_heap_insert function located in ext/spl/spl_heap.c, which is part of PHP's heap data structure implementation. The flaw manifests when a failed SplMinHeap::compare operation occurs, creating a scenario where memory that has been freed is subsequently accessed, leading to potential code execution. This type of vulnerability falls under the CWE-416 category of Use After Free, which is classified as a serious memory safety issue that can be exploited to gain arbitrary code execution on vulnerable systems. The vulnerability is particularly concerning because it can be triggered remotely through web-based PHP applications, making it a significant threat to web server security.
The technical exploitation of this vulnerability occurs when an attacker manipulates the SplMinHeap::compare operation to force a failure condition that results in memory deallocation. During the heap insertion process, PHP maintains internal heap structures that manage memory allocation and deallocation. When the comparison operation fails, the heap management code may attempt to free memory that is subsequently accessed in an improper manner. This creates a race condition where freed memory can be reallocated and accessed by malicious code, potentially allowing attackers to inject and execute arbitrary code with the privileges of the PHP process. The vulnerability specifically targets the heap management functions that handle pointer operations, making it particularly dangerous in environments where PHP processes handle untrusted input data.
The operational impact of CVE-2015-4116 extends beyond simple code execution, as it can be leveraged to achieve complete system compromise in vulnerable environments. Attackers can exploit this vulnerability through web applications that utilize PHP heap structures, particularly those that process user-supplied data through SplMinHeap objects. The remote execution capability means that attackers do not need physical access to the server, making this vulnerability particularly attractive for widespread exploitation. This vulnerability directly aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, and T1190 for Exploit Public-Facing Application, as it enables attackers to execute arbitrary code on web servers through web-based attack vectors. The exploitation process typically involves crafting specific input data that causes the heap management functions to behave in unexpected ways, leading to memory corruption that can be leveraged for privilege escalation.
Mitigation strategies for CVE-2015-4116 primarily involve immediate patching of affected PHP installations to versions 5.5.27 or 5.6.11 and later. System administrators should prioritize updating their PHP environments and validate that all web applications are running on patched versions. Additionally, implementing input validation and sanitization measures can help reduce the attack surface by preventing malicious data from reaching heap management functions. Network-level protections such as web application firewalls can provide additional defense-in-depth measures, though they should not be considered a replacement for proper patching. Organizations should also monitor their PHP applications for improper heap usage patterns and implement runtime protections where possible. The vulnerability demonstrates the importance of proper memory management in interpreted languages and underscores the need for regular security updates in web application environments. This vulnerability serves as a reminder of the critical nature of heap management in preventing memory safety issues that can lead to remote code execution in web server environments.