CVE-2007-4825 in PHP
Summary
by MITRE
Directory traversal vulnerability in PHP 5.2.4 and earlier allows attackers to bypass open_basedir restrictions and possibly execute arbitrary code via a .. (dot dot) in the dl function.
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Analysis
by VulDB Data Team • 07/27/2019
The vulnerability identified as CVE-2007-4825 represents a critical directory traversal flaw affecting PHP versions 5.2.4 and earlier, specifically within the dynamic loading functionality of the language. This vulnerability resides in the dl function which is designed to load dynamic extensions at runtime, creating a potential attack surface that can be exploited by malicious actors seeking to circumvent security restrictions. The issue manifests when the dl function processes path traversal sequences such as .. (dot dot) characters, allowing attackers to navigate outside the intended directory boundaries and access restricted files or execute unauthorized operations. The vulnerability directly impacts the security model of PHP installations by undermining the open_basedir directive, a crucial mechanism for restricting file access to specific directories and preventing unauthorized file system operations. This flaw enables attackers to bypass fundamental security controls that are typically in place to limit the scope of file operations within PHP applications, potentially leading to complete system compromise.
The technical exploitation of this vulnerability occurs through the manipulation of the dl function's argument handling, where the .. sequence can be used to traverse parent directories and access files outside the intended scope. When PHP processes a dynamic library load request containing directory traversal sequences, the underlying implementation fails to properly sanitize or validate the path components, allowing the attacker to specify arbitrary file paths. The vulnerability is particularly dangerous because it combines path traversal with dynamic loading capabilities, potentially enabling attackers to load malicious shared libraries or access sensitive system files that should normally be restricted. The flaw essentially creates a bypass mechanism that allows the dl function to operate outside the confines of the open_basedir restrictions, which are typically configured to limit file access to specific directories and prevent unauthorized file system operations.
From an operational perspective, this vulnerability presents a severe risk to web applications running vulnerable PHP versions, as it can enable attackers to execute arbitrary code on the target system. The impact extends beyond simple file access violations to potentially full system compromise, as attackers can leverage the dl function to load malicious code libraries and execute commands with the privileges of the web server process. This vulnerability is particularly concerning in shared hosting environments where multiple applications might be running on the same server, as it could allow an attacker to access files belonging to other users or applications. The attack vector is relatively straightforward, requiring only a properly crafted dl function call that includes directory traversal sequences, making it accessible to attackers with moderate technical skills. The vulnerability also affects the integrity of the application environment, as it allows for the potential modification of critical system components through the dynamic loading mechanism.
Mitigation strategies for CVE-2007-4825 primarily focus on immediate version upgrades to PHP 5.2.5 or later, where the vulnerability has been addressed through proper path validation and sanitization within the dl function implementation. System administrators should also implement additional security measures such as disabling the dl function entirely through php.ini configuration, which removes the attack surface entirely by preventing dynamic library loading. The open_basedir directive should be configured with strict path restrictions and regularly audited to ensure proper enforcement, while comprehensive monitoring should be implemented to detect suspicious file access patterns or attempts to load dynamic libraries. Organizations should also consider implementing web application firewalls to detect and block malicious requests containing directory traversal sequences, and conduct regular security assessments to identify any remaining vulnerabilities in their PHP implementations. This vulnerability aligns with CWE-22 directory traversal weaknesses and can be mapped to ATT&CK technique T1059.007 for dynamic code injection, highlighting the importance of proper input validation and privilege separation in preventing such exploits.