CVE-2008-5625 in PHP
Summary
by MITRE
PHP 5 before 5.2.7 does not enforce the error_log safe_mode restrictions when safe_mode is enabled through a php_admin_flag setting in httpd.conf, which allows context-dependent attackers to write to arbitrary files by placing a "php_value error_log" entry in a .htaccess file.
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Analysis
by VulDB Data Team • 11/11/2024
This vulnerability exists in php versions prior to 5.2.7 where the error_log directive fails to respect safe_mode restrictions when safe_mode is configured via php_admin_flag in httpd.conf. The flaw represents a critical privilege escalation issue that allows attackers to bypass security controls designed to restrict file operations within the php environment. When safe_mode is enabled through the httpd configuration using php_admin_flag, the system should enforce strict file access controls, but the error_log functionality ignores these restrictions. This creates a dangerous situation where attackers can manipulate the error_log directive through .htaccess files, effectively circumventing the intended security boundaries that should prevent unauthorized file access.
The technical implementation of this vulnerability relies on the improper handling of configuration directives within the php runtime environment. Specifically, when php is configured with safe_mode enabled through httpd's php_admin_flag directive, the error_log parameter should be restricted to prevent arbitrary file writes. However, the vulnerability allows attackers to set error_log to any file path by adding a php_value error_log entry in a .htaccess file, which is processed after the main php configuration. This creates a context-dependent attack vector where the attacker can leverage the web server's configuration parsing mechanism to inject malicious file paths into the error_log directive. The flaw essentially creates a backdoor through which attackers can write to any file that the web server process has permissions to access, regardless of the safe_mode restrictions that should normally apply.
The operational impact of this vulnerability is severe as it enables attackers to perform unauthorized file operations that could lead to complete system compromise. An attacker with access to upload or modify .htaccess files can use this vulnerability to write malicious content to files that would normally be protected by safe_mode restrictions. This could include writing web shells, modifying existing application files, or creating persistent backdoors within the web application environment. The vulnerability is particularly dangerous because it operates at the intersection of web server configuration and php runtime behavior, making it difficult to detect and remediate. The context-dependent nature means that the attack only works when the specific configuration pattern exists, but once exploited, it can provide persistent access to the compromised system.
The vulnerability maps directly to CWE-276, which describes improper file permissions, and aligns with ATT&CK technique T1548.001 for privilege escalation through configuration modifications. Organizations should immediately upgrade to php version 5.2.7 or later to resolve this issue, as the vulnerability is not limited to specific operating systems or configurations but affects any environment where php is configured with safe_mode enabled through httpd. Mitigation strategies include implementing proper file access controls for .htaccess files, monitoring for unauthorized configuration changes, and ensuring that web server configurations properly restrict the ability to modify php directives through user-accessible files. Additionally, organizations should consider implementing web application firewalls to detect and prevent suspicious .htaccess modifications, and conduct regular security audits to identify systems that may still be running vulnerable php versions. The vulnerability demonstrates the critical importance of proper configuration management and the potential risks that arise when different security mechanisms fail to properly interoperate within complex web application environments.