CVE-2006-2563 in PHP
Summary
by MITRE
The cURL library (libcurl) in PHP 4.4.2 and 5.1.4 allows attackers to bypass safe mode and read files via a file:// request containing null characters.
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Analysis
by VulDB Data Team • 06/23/2019
The cURL library vulnerability identified as CVE-2006-2563 represents a critical security flaw in PHP versions 4.4.2 and 5.1.4 that fundamentally undermines the safe mode protection mechanisms designed to restrict file access operations. This vulnerability specifically targets the file:// protocol handler within libcurl, which is integrated into PHP's web development environment and commonly used for retrieving resources from various protocols including local files. The flaw manifests when attackers construct malicious file:// URLs containing null characters that can manipulate the underlying file access routines.
The technical implementation of this vulnerability stems from improper handling of null characters within the file URI parsing logic of the cURL library. When PHP processes a file:// request with null bytes embedded in the path, the null termination characters interfere with the standard string processing functions that normally validate and sanitize file access requests. This creates a condition where the safe mode restrictions intended to prevent unauthorized file access can be circumvented, allowing attackers to traverse the file system and read arbitrary files that should normally be protected from access. The vulnerability operates at the level of input validation and string handling, making it particularly dangerous as it exploits fundamental assumptions about how file paths should be processed.
The operational impact of this vulnerability extends beyond simple file reading capabilities to encompass potential system compromise and data exfiltration scenarios. Attackers can leverage this flaw to access sensitive system files, configuration data, database credentials, and other confidential information stored on the web server. The bypass of safe mode protection means that even in restricted environments where PHP is configured to limit file access, attackers can still gain unauthorized access to critical system resources. This vulnerability particularly affects web applications running on vulnerable PHP versions where file operations are performed through cURL functions, creating a significant risk for any system that processes user-supplied URLs or file paths without proper validation.
Security practitioners should implement immediate mitigations including upgrading to patched versions of PHP where this vulnerability has been resolved, applying the appropriate security patches released by the PHP development team, and implementing additional input validation measures that explicitly check for null characters in file paths and URLs. Organizations should also consider implementing network-level protections such as web application firewalls that can detect and block suspicious file:// requests containing null bytes. The vulnerability aligns with CWE-170, which addresses improper handling of null terminators in string operations, and represents a clear example of how protocol handler flaws can be exploited to bypass security controls. This issue also maps to ATT&CK technique T1059.007 for command and scripting interpreter and T1566 for credential access through exploitation of vulnerable software components. Organizations must prioritize this vulnerability remediation as it provides attackers with direct access to system resources that should remain protected under normal security configurations.