CVE-2015-6836 in Mac OS X
Summary
by MITRE
The SoapClient __call method in ext/soap/soap.c in PHP before 5.4.45, 5.5.x before 5.5.29, and 5.6.x before 5.6.13 does not properly manage headers, which allows remote attackers to execute arbitrary code via crafted serialized data that triggers a "type confusion" in the serialize_function_call function.
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Analysis
by VulDB Data Team • 06/24/2022
The vulnerability identified as CVE-2015-6836 represents a critical type confusion flaw within PHP's SOAP extension that affects multiple versions of the PHP runtime environment. This vulnerability specifically resides in the SoapClient __call method implementation located in ext/soap/soap.c, where improper header management creates a pathway for remote code execution through crafted serialized data. The flaw stems from insufficient validation and handling of SOAP headers during the serialization process, creating conditions where attackers can manipulate the data flow to achieve unintended execution behavior.
The technical exploitation of this vulnerability leverages type confusion within the serialize_function_call function, which occurs when PHP's internal type system becomes confused about the expected data types during serialization operations. When a malicious user crafts specific serialized data containing crafted headers, the SoapClient processes this data through the vulnerable code path where the type confusion manifests. This allows attackers to manipulate the execution flow and potentially execute arbitrary code on the target system with the privileges of the PHP process. The vulnerability is particularly dangerous because it operates at the serialization layer, where data from untrusted sources is processed and interpreted by the PHP runtime.
From an operational impact perspective, this vulnerability enables remote attackers to achieve full system compromise without requiring authentication or privileged access. The attack surface is broad as any application using PHP's SOAP client functionality becomes potentially vulnerable, particularly web applications that process SOAP requests from external sources. The vulnerability can be exploited through various attack vectors including web services, API endpoints, or any interface that utilizes the SoapClient __call method. The execution of arbitrary code provides attackers with capabilities to install backdoors, exfiltrate data, escalate privileges, or establish persistent access to affected systems. This aligns with ATT&CK technique T1059.007 for command and script interpreter execution, as the vulnerability enables arbitrary code execution through the PHP interpreter.
The root cause of this vulnerability can be classified under CWE-122 as "Heap-based Buffer Overflow" or more specifically CWE-787 as "Out-of-bounds Write" when considering the type confusion aspects. The improper handling of serialized data structures in the SOAP extension creates a condition where memory operations exceed expected boundaries, allowing attackers to manipulate program execution flow. Organizations using PHP applications that rely on SOAP functionality are particularly at risk, especially those with exposed web services or APIs that accept external SOAP requests. The vulnerability affects the core PHP runtime rather than specific applications, making it a widespread concern across the PHP ecosystem.
Mitigation strategies for CVE-2015-6836 primarily involve immediate patching of affected PHP versions to the recommended secure releases including PHP 5.4.45, 5.5.29, and 5.6.13 or later. Organizations should also implement network-level restrictions to limit access to SOAP endpoints and consider disabling SOAP functionality when not required. Input validation and sanitization of all SOAP headers and data should be enforced, along with monitoring for unusual patterns in SOAP request processing. Security teams should conduct comprehensive vulnerability assessments to identify applications using vulnerable SoapClient implementations and ensure proper patch management procedures are in place to prevent similar vulnerabilities from occurring in the future.