CVE-2007-4850 in PHP
Summary
by MITRE
curl/interface.c in the cURL library (aka libcurl) in PHP 5.2.4 and 5.2.5 allows context-dependent attackers to bypass safe_mode and open_basedir restrictions and read arbitrary files via a file:// request containing a \x00 sequence, a different vulnerability than CVE-2006-2563.
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Analysis
by VulDB Data Team • 04/26/2025
The vulnerability described in CVE-2007-4850 represents a critical security flaw in the cURL library implementation within PHP versions 5.2.4 and 5.2.5. This issue specifically affects the curl/interface.c component of the library and exploits a context-dependent weakness that allows malicious actors to circumvent fundamental PHP security mechanisms. The vulnerability operates through a file:// request that incorporates a null byte sequence, creating a pathway for unauthorized file access that bypasses the intended security boundaries.
The technical implementation of this vulnerability stems from how the cURL library processes file:// URLs when null bytes are present in the request string. When PHP's safe_mode and open_basedir restrictions are enabled, these mechanisms are designed to prevent scripts from accessing files outside of designated directories, thereby limiting potential damage from malicious file operations. However, the presence of null byte sequences in file:// requests causes the library to misinterpret the file path, effectively truncating the path at the null byte location and allowing access to files that should otherwise be restricted.
This flaw directly impacts the integrity of PHP's security model by undermining the fundamental principle of path validation and access control. The vulnerability enables attackers to read arbitrary files on the server filesystem, potentially exposing sensitive data including configuration files, database credentials, user information, and other confidential resources that should remain protected by the safe_mode and open_basedir restrictions. The operational impact extends beyond simple file reading, as it can lead to complete system compromise when combined with other vulnerabilities or when sensitive files are accessed.
The vulnerability's classification aligns with CWE-22, which addresses Improper Limitation of a Pathname to a Restricted Directory, and demonstrates how improper input handling can result in privilege escalation and unauthorized data access. From an ATT&CK perspective, this vulnerability maps to T1059.007 for Command and Scripting Interpreter: Python, though in this case the attack vector involves HTTP protocol manipulation rather than direct command execution. The issue represents a classic example of how seemingly benign input processing can create security holes when null byte handling is not properly managed in network protocol implementations.
Organizations affected by this vulnerability should immediately upgrade to PHP versions 5.2.6 or later, where the issue has been patched. Additionally, administrators should implement immediate monitoring for unusual file access patterns and ensure that all PHP installations are regularly updated with the latest security patches. The mitigation strategy should include disabling unnecessary file access functions, implementing robust input validation for all user-supplied data, and maintaining comprehensive logging of file operations to detect potential exploitation attempts. Security teams should also consider implementing network-based intrusion detection systems that can identify null byte sequences in HTTP requests and alert on suspicious patterns that may indicate exploitation attempts.