CVE-2016-9137 in PHP
Summary
by MITRE
Use-after-free vulnerability in the CURLFile implementation in ext/curl/curl_file.c in PHP before 5.6.27 and 7.x before 7.0.12 allows remote attackers to cause a denial of service or possibly have unspecified other impact via crafted serialized data that is mishandled during __wakeup processing.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 10/27/2022
The CVE-2016-9137 vulnerability represents a critical use-after-free flaw in PHP's cURL file handling implementation that affects versions prior to 5.6.27 and 7.0.12. This vulnerability exists within the ext/curl/curl_file.c source file where the CURLFile class processes serialized data during object reconstruction. The flaw manifests when PHP encounters crafted serialized data containing CURLFile objects that are improperly handled during the __wakeup magic method execution, creating conditions where freed memory locations can be accessed or manipulated by remote attackers.
The technical exploitation of this vulnerability leverages PHP's serialization mechanism to craft malicious payloads that trigger improper memory management during object deserialization. When a CURLFile object is reconstructed from serialized data, the __wakeup method processes the object's internal state without proper validation of memory references, leading to a scenario where freed memory blocks are accessed or overwritten. This use-after-free condition can result in memory corruption that may allow attackers to execute arbitrary code or cause system instability through denial of service attacks. The vulnerability is particularly dangerous because it operates at the PHP interpreter level where memory management and object lifecycle handling are critical components of the application's security posture.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable remote code execution in certain environments where attackers can control the serialized input. The flaw affects PHP applications that process untrusted data through serialization mechanisms, particularly those utilizing cURL functionality for file operations or HTTP requests. Attackers can craft serialized objects containing malicious CURLFile references that, when processed by vulnerable PHP versions, create exploitable memory conditions. This vulnerability aligns with CWE-416, which describes the use of freed memory condition, and represents a classic example of improper memory management in interpreted languages where object lifecycle management is handled automatically by the runtime.
Organizations affected by this vulnerability should immediately upgrade to PHP versions 5.6.27 or 7.0.12 and later, as these releases contain patches that properly validate memory references during __wakeup processing. Additional mitigations include implementing strict input validation for serialized data, avoiding the processing of untrusted serialized objects, and monitoring for unusual memory access patterns or denial of service attempts. Security teams should also consider implementing application firewalls or intrusion detection systems that can identify and block malicious serialization patterns. The vulnerability demonstrates the importance of proper memory management in interpreted languages and highlights the need for regular security updates to address memory corruption issues that can lead to privilege escalation or complete system compromise. Organizations should conduct comprehensive vulnerability assessments to identify applications using affected PHP versions and ensure proper patching across all environments to prevent exploitation.