CVE-2007-0911 in PHP
Summary
by MITRE
Off-by-one error in the str_ireplace function in PHP 5.2.1 might allow context-dependent attackers to cause a denial of service (crash).
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Analysis
by VulDB Data Team • 04/10/2025
The vulnerability identified as CVE-2007-0911 represents a critical off-by-one error within the str_ireplace function implementation in PHP version 5.2.1. This type of error occurs when a program attempts to access memory outside the bounds of a buffer or string, creating a condition that can lead to unpredictable behavior including application crashes. The issue specifically affects the case-insensitive string replacement functionality that PHP provides for developers working with text processing tasks. The vulnerability manifests when the str_ireplace function processes certain input patterns that trigger memory access violations due to improper boundary checking in the underlying implementation.
The technical flaw stems from inadequate validation of string boundaries during the replacement operation, where the function fails to properly account for the exact memory locations when processing case-insensitive matches. This particular implementation flaw allows attackers to craft specific input sequences that cause the PHP interpreter to attempt memory access at invalid addresses. The vulnerability is context-dependent meaning that successful exploitation requires specific conditions related to how the vulnerable function is called within the application code. Attackers can leverage this weakness by providing carefully crafted input that triggers the problematic code path, causing the PHP process to terminate unexpectedly and resulting in a denial of service condition.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect any web application running on PHP 5.2.1 that utilizes the str_ireplace function for processing user input. When exploited, the vulnerability leads to application crashes that can be leveraged for denial of service attacks against web servers hosting PHP applications. This creates significant risk for websites and web services that depend on PHP for dynamic content generation, as a single malicious request could cause the entire application to become unavailable. The vulnerability is particularly concerning because it can be triggered through normal user input processing without requiring special privileges or complex attack vectors.
Mitigation strategies for CVE-2007-0911 primarily focus on immediate remediation through version updates, as PHP 5.2.1 is an outdated version that has been superseded by multiple security patches and newer releases. Organizations should prioritize upgrading to supported PHP versions that contain fixes for this and similar memory handling vulnerabilities. Additionally, input validation measures can provide temporary protection by sanitizing user input before it reaches the vulnerable function, though this approach does not address the root cause. Implementing proper error handling and monitoring mechanisms can help detect exploitation attempts, while application firewalls and intrusion detection systems can provide additional layers of protection. This vulnerability aligns with CWE-129 which describes improper validation of array indices and CWE-787 which covers out-of-bounds write conditions, while the attack pattern follows techniques described in the ATT&CK framework under process injection and denial of service categories. The vulnerability demonstrates the importance of proper memory management in interpreted languages and highlights the critical need for regular security updates in web application environments.