CVE-2007-1453 in PHP
Summary
by MITRE
Buffer underflow in the PHP_FILTER_TRIM_DEFAULT macro in the filtering extension (ext/filter) in PHP 5.2.0 allows context-dependent attackers to execute arbitrary code by calling filter_var with certain modes such as FILTER_VALIDATE_INT, which causes filter to write a null byte in whitespace that precedes the buffer.
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Analysis
by VulDB Data Team • 04/23/2025
The vulnerability described in CVE-2007-1453 represents a critical buffer underflow condition within PHP's filtering extension that was present in PHP version 5.2.0. This flaw exists within the PHP_FILTER_TRIM_DEFAULT macro implementation and specifically affects how the filter_var function processes certain input validation modes including FILTER_VALIDATE_INT. The underlying technical mechanism involves the improper handling of memory boundaries when processing whitespace characters preceding buffer contents, creating a condition where a null byte can be written into memory locations that should remain untouched. This memory corruption vulnerability stems from inadequate bounds checking within the filter extension's internal processing routines, allowing attackers to manipulate memory layout through carefully crafted input sequences.
The operational impact of this vulnerability extends beyond simple code execution privileges, as it enables context-dependent attackers to potentially gain arbitrary code execution capabilities on systems running vulnerable PHP versions. Attackers can exploit this weakness by invoking filter_var with specific modes that trigger the flawed memory handling behavior, particularly when processing integer validation inputs. The vulnerability's exploitation requires knowledge of the specific memory layout and the ability to craft input that will cause the buffer underflow condition to manifest. The attack vector operates through the PHP filter extension's processing pipeline where the memory corruption can be leveraged to overwrite critical memory locations, potentially leading to privilege escalation or complete system compromise. This type of vulnerability aligns with CWE-121, which describes buffer underflow conditions, and represents a classic example of memory safety issues that have historically led to severe security consequences in web applications.
The exploitation of this vulnerability demonstrates the importance of proper input validation and memory boundary checking in server-side scripting environments. Systems running PHP 5.2.0 are particularly at risk because the vulnerability exists in the core filtering functionality that many applications rely upon for data validation. The attack scenario typically involves an attacker submitting specially crafted input to a web application that uses filter_var with FILTER_VALIDATE_INT or similar modes, which then triggers the memory corruption. This vulnerability also relates to ATT&CK technique T1059.007, which involves the use of scripting languages for execution, and T1190, which covers exploitation of remote services through input validation flaws. Organizations should consider implementing immediate mitigations including updating to patched PHP versions, applying security patches, and implementing input sanitization measures to prevent exploitation of this class of vulnerability that affects the fundamental data validation mechanisms within web applications.
The broader implications of this vulnerability highlight the critical nature of maintaining up-to-date software components in web application environments. PHP's filtering extension serves as a foundational component for many security validation processes, making this type of memory corruption particularly dangerous as it can be leveraged across multiple application contexts. The vulnerability's persistence in the filtering extension demonstrates how seemingly routine data validation functions can contain critical security flaws that affect the entire application stack. Security practitioners should recognize that buffer underflow conditions like this one often indicate deeper architectural issues with memory management and input processing that may affect other components of the same software ecosystem. This vulnerability reinforces the importance of comprehensive security testing including memory safety analysis and regular vulnerability assessments to identify and remediate similar issues before they can be exploited in production environments.