CVE-2015-4598 in PHP
Summary
by MITRE
PHP before 5.4.42, 5.5.x before 5.5.26, and 5.6.x before 5.6.10 does not ensure that pathnames lack %00 sequences, which might allow remote attackers to read or write to arbitrary files via crafted input to an application that calls (1) a DOMDocument save method or (2) the GD imagepsloadfont function, as demonstrated by a filename\0.html attack that bypasses an intended configuration in which client users may write to only .html files.
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Analysis
by VulDB Data Team • 05/22/2022
The vulnerability described in CVE-2015-4598 represents a critical file path manipulation issue affecting multiple versions of the PHP scripting language. This flaw exists within the core file handling mechanisms of PHP, specifically when processing file paths that contain null byte sequences. The vulnerability stems from insufficient validation of pathname inputs, allowing malicious actors to inject null bytes into file operations that should be restricted to specific file types. The issue impacts PHP versions prior to 5.4.42, 5.5.26, and 5.6.10, making it a widespread concern affecting numerous web applications that rely on PHP for server-side processing.
The technical implementation of this vulnerability occurs when applications utilize DOMDocument save methods or the GD imagepsloadfont function without proper input sanitization. When these functions process file paths containing null byte sequences, the PHP interpreter may interpret the null byte as a string terminator, effectively truncating the filename at that point. This behavior allows attackers to bypass intended file extension restrictions and access arbitrary files on the server. The attack vector demonstrated in the vulnerability involves crafting filenames with null bytes followed by .html extensions, which can deceive applications configured to only accept .html files from client uploads. This manipulation enables unauthorized read or write operations to files outside the intended scope, potentially leading to data exposure, file corruption, or complete system compromise.
The operational impact of CVE-2015-4598 extends beyond simple file access violations and represents a significant escalation in attack capabilities for remote adversaries. Applications that accept user-provided filenames for processing, particularly those involving document or image manipulation, become vulnerable to this attack. The vulnerability can be exploited to read sensitive system files, modify critical application components, or establish persistent access through file injection attacks. The implications are particularly severe for web applications that process user uploads or allow dynamic file creation, as the attack can bypass security controls designed to restrict file types and locations. This vulnerability aligns with CWE-174, which describes weaknesses in input handling that fail to properly process null bytes, and can be categorized under ATT&CK technique T1059 for command and scripting interpreter usage, as successful exploitation may enable further malicious activities.
Organizations affected by this vulnerability should prioritize immediate patching of their PHP installations to versions that address the null byte handling issue. The recommended mitigation strategy involves upgrading to PHP 5.4.42, 5.5.26, or 5.6.10, depending on the current version in use. Additionally, application-level defenses should be implemented to validate and sanitize all user-provided filenames, ensuring that null bytes are rejected or properly escaped before processing. Input validation should be enforced at multiple layers, including both server-side and client-side controls, to prevent malicious payloads from reaching vulnerable PHP functions. Security monitoring should be enhanced to detect suspicious file operations, particularly those involving unusual filename patterns or attempts to access restricted file types. This vulnerability demonstrates the critical importance of proper input validation and the potential for seemingly minor implementation flaws to result in significant security breaches.