CVE-2011-4153 in PHP
Summary
by MITRE
PHP 5.3.8 does not always check the return value of the zend_strndup function, which might allow remote attackers to cause a denial of service (NULL pointer dereference and application crash) via crafted input to an application that performs strndup operations on untrusted string data, as demonstrated by the define function in zend_builtin_functions.c, and unspecified functions in ext/soap/php_sdl.c, ext/standard/syslog.c, ext/standard/browscap.c, ext/oci8/oci8.c, ext/com_dotnet/com_typeinfo.c, and main/php_open_temporary_file.c.
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Analysis
by VulDB Data Team • 10/19/2024
The vulnerability described in CVE-2011-4153 represents a critical NULL pointer dereference issue affecting PHP 5.3.8 and potentially other versions within the 5.3.x series. This flaw stems from insufficient error handling within the zend_strndup function implementation, which is a fundamental string duplication utility used throughout the PHP core and its extensions. The vulnerability manifests when applications process untrusted input data through functions that internally invoke zend_strndup without proper validation of its return value. This particular weakness falls under CWE-476 which specifically addresses NULL pointer dereference conditions, making it a significant concern for application stability and security.
The technical exploitation of this vulnerability occurs when remote attackers craft malicious input that triggers the zend_strndup function to return a NULL pointer, which is then subsequently dereferenced by the calling application. The attack surface includes multiple PHP extensions and core functions, with the exploit demonstrated through the define function in zend_builtin_functions.c and additional functions across SOAP, syslog, browscap, oci8, com_dotnet, and temporary file handling components. This widespread presence across different PHP modules indicates a systemic issue in the error handling approach for string operations within the PHP engine, particularly in how it manages memory allocation failures and subsequent pointer validation.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can lead to complete application crashes and system instability. When a NULL pointer dereference occurs, it typically results in a segmentation fault that terminates the PHP process, effectively causing a denial of service for all users of that application. The vulnerability is particularly dangerous in web server environments where PHP applications handle user input, as attackers can systematically crash web applications by submitting carefully crafted strings that trigger the problematic code paths. This makes it a preferred target for attackers seeking to disrupt services without necessarily gaining unauthorized access to system resources.
Mitigation strategies for CVE-2011-4153 should focus on immediate patching of affected PHP installations to versions that properly handle zend_strndup return values and validate memory allocations. Organizations should implement comprehensive input validation measures that sanitize all user-provided data before processing, particularly in areas where string operations are performed. Additionally, deploying intrusion detection systems that monitor for unusual patterns of NULL pointer dereference attempts can help detect exploitation attempts. The vulnerability aligns with ATT&CK technique T1499 which covers endpoint denial of service attacks, and organizations should consider implementing application whitelisting and process monitoring to prevent exploitation. Regular security assessments of PHP applications and extensions should be conducted to identify similar error handling deficiencies that could lead to comparable vulnerabilities in the future.