CVE-2016-6296 in macOS
Summary
by MITRE
Integer signedness error in the simplestring_addn function in simplestring.c in xmlrpc-epi through 0.54.2, as used in PHP before 5.5.38, 5.6.x before 5.6.24, and 7.x before 7.0.9, allows remote attackers to cause a denial of service (heap-based buffer overflow) or possibly have unspecified other impact via a long first argument to the PHP xmlrpc_encode_request function.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-6296 represents a critical integer signedness error within the xmlrpc-epi library component that affects multiple PHP versions. This flaw exists in the simplestring_addn function located in simplestring.c, which serves as a core component in the XML-RPC encoding process. The vulnerability manifests when the PHP xmlrpc_encode_request function processes a malformed first argument, creating conditions that can lead to heap-based buffer overflow conditions. The integer signedness error occurs when unsigned integer values are incorrectly interpreted as signed integers during arithmetic operations, allowing attackers to manipulate memory boundaries through crafted input parameters.
The technical exploitation of this vulnerability leverages the improper handling of integer values during string manipulation operations within the XML-RPC encoding process. When the simplestring_addn function processes input data, it performs calculations that assume signed integer behavior while receiving unsigned integer values, creating a scenario where buffer boundaries can be exceeded. This misalignment between expected and actual integer types allows attackers to manipulate memory allocation and access patterns, potentially leading to heap corruption. The vulnerability operates at the intersection of memory management and input validation, where the lack of proper bounds checking combined with incorrect integer type interpretation creates exploitable conditions.
From an operational perspective, this vulnerability presents significant risks to web applications that utilize PHP's XML-RPC functionality for remote procedure calls and web service communications. The impact extends beyond simple denial of service to potentially enable more severe consequences including arbitrary code execution or system compromise. Attackers can exploit this vulnerability by crafting specially formatted XML-RPC requests with extended first arguments that trigger the buffer overflow condition. The vulnerability affects a broad range of PHP installations, spanning major version lines including 5.5, 5.6, and 7.0, making it particularly dangerous for organizations with diverse PHP environments. The heap-based buffer overflow creates opportunities for memory corruption that can be leveraged to execute malicious code or cause system instability.
Security mitigations for CVE-2016-6296 primarily focus on immediate patching of affected PHP versions to the corrected releases that address the integer signedness error. Organizations should implement comprehensive input validation for all XML-RPC requests and consider implementing network-level controls to restrict access to XML-RPC endpoints. The vulnerability aligns with CWE-190, which specifically addresses integer overflow and underflow conditions, and can be mapped to ATT&CK technique T1203 for exploitation of remote services. Additionally, implementing application firewalls and intrusion detection systems can help detect and prevent exploitation attempts targeting this specific vulnerability pattern. Regular security assessments and vulnerability scanning should be conducted to identify systems running vulnerable PHP versions and ensure timely remediation through official security updates from PHP development teams.