CVE-2024-4577 in PHP
Summary
by MITRE • 06/09/2024
In PHP versions 8.1.* before 8.1.29, 8.2.* before 8.2.20, 8.3.* before 8.3.8, when using Apache and PHP-CGI on Windows, if the system is set up to use certain code pages, Windows may use "Best-Fit" behavior to replace characters in command line given to Win32 API functions. PHP CGI module may misinterpret those characters as PHP options, which may allow a malicious user to pass options to PHP binary being run, and thus reveal the source code of scripts, run arbitrary PHP code on the server, etc.
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Analysis
by VulDB Data Team • 08/01/2025
This vulnerability exists in PHP versions 8.1.x before 8.1.29, 8.2.x before 8.2.20, and 8.3.x before 8.3.8 when running under Apache with PHP-CGI on Windows systems. The flaw stems from how Windows handles certain code pages and employs "Best-Fit" character replacement behavior in Win32 API functions. When PHP-CGI processes command line arguments, it fails to properly account for these character substitutions that occur during the Windows API call execution. This misinterpretation creates a path for malicious input to be treated as PHP command line options rather than standard input parameters. The vulnerability specifically affects Windows environments where certain code page configurations trigger the Best-Fit replacement mechanism, allowing attackers to manipulate how PHP processes command line arguments through the Windows API layer. This represents a critical security issue that can be leveraged for remote code execution and information disclosure.
The technical implementation of this vulnerability involves the interaction between PHP's CGI module and Windows system APIs. When PHP-CGI receives input through Apache on Windows, the system's code page handling can cause certain characters to be automatically replaced with alternative characters that have different meanings in the PHP option parsing process. This Best-Fit behavior is part of Windows' legacy character encoding handling and specifically affects how non-ASCII characters are mapped when they cannot be directly represented in the target code page. PHP's command line argument parser does not properly sanitize or validate these character substitutions, leading to potential option injection where attacker-controlled characters can be interpreted as valid PHP command line switches. This creates a direct pathway for privilege escalation and arbitrary code execution through carefully crafted input that exploits the Windows API character mapping behavior.
The operational impact of this vulnerability is severe and multifaceted, encompassing both information disclosure and remote code execution capabilities. An attacker can exploit this flaw to execute arbitrary PHP code on the server, potentially gaining full control over the web application environment. The vulnerability also enables source code disclosure, allowing attackers to read sensitive PHP script contents that may contain database credentials, encryption keys, or other confidential information. Additionally, the attack can be performed remotely without requiring authentication, making it particularly dangerous for publicly accessible web applications. The vulnerability affects all PHP versions within the specified ranges when deployed on Windows systems with Apache and PHP-CGI, creating widespread exposure across numerous web servers and applications. This represents a privilege escalation vector that can be exploited by attackers with minimal technical requirements, as the vulnerability operates at the system call level rather than requiring complex exploitation techniques.
The vulnerability aligns with CWE-15 (External Control of System or Configuration Setting) and CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component) in the Common Weakness Enumeration catalog. It also maps to ATT&CK technique T1190 (Exploit Public-Facing Application) and T1059 (Command and Scripting Interpreter) within the MITRE ATT&CK framework. Organizations should immediately apply patches to PHP versions 8.1.29, 8.2.20, and 8.3.8, or upgrade to newer stable releases. Additional mitigations include implementing proper input validation and sanitization at the application level, restricting Apache's access to PHP-CGI modules, and monitoring for suspicious command line argument patterns in web server logs. Network-level protections such as web application firewalls can help detect and block exploitation attempts, while system administrators should review code page configurations on Windows servers to minimize the likelihood of triggering Best-Fit character replacement behavior. The vulnerability demonstrates the critical importance of considering platform-specific behaviors in security implementations, particularly when dealing with legacy character encoding mechanisms in Windows environments.