CVE-2009-0754 in PHP
Summary
by MITRE
PHP 4.4.4, 5.1.6, and other versions, when running on Apache, allows local users to modify behavior of other sites hosted on the same web server by modifying the mbstring.func_overload setting within .htaccess, which causes this setting to be applied to other virtual hosts on the same server.
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Analysis
by VulDB Data Team • 01/29/2025
This vulnerability exists in PHP versions 4.4.4 and 5.1.6 when operating within an Apache web server environment. The core issue stems from how PHP handles multibyte string function overloading settings, specifically the mbstring.func_overload directive. When this setting is configured through a .htaccess file, it creates a cross-site contamination problem that affects all virtual hosts sharing the same Apache server instance. The vulnerability represents a critical configuration management flaw that undermines the isolation typically maintained between different web applications hosted on the same server infrastructure.
The technical mechanism of this vulnerability involves the Apache server's handling of per-directory configuration files. When a .htaccess file containing the mbstring.func_overload setting is processed in a specific directory, Apache propagates this configuration change across all virtual hosts that share the same server context. This occurs because PHP's configuration directives set through .htaccess files are not properly scoped to individual virtual hosts, creating a situation where local users can manipulate server-wide settings that affect other tenants. The flaw essentially allows a malicious user to modify system behavior that should remain isolated to their own virtual host environment, leading to potential information disclosure and service disruption across multiple sites.
The operational impact of this vulnerability is significant for shared hosting environments and multi-tenant web server configurations. Local attackers who gain access to write permissions in any directory on the server can modify the mbstring.func_overload setting to redirect function calls to different string handling implementations. This can result in unexpected behavior where legitimate web applications might start executing with altered string processing characteristics, potentially leading to data corruption, information leakage, or even remote code execution depending on how the affected applications handle string operations. The vulnerability particularly affects applications that rely heavily on multibyte character processing, making it a serious concern for internationalized web applications.
Organizations should implement immediate mitigations including restricting write permissions on directories where .htaccess files can be placed, ensuring proper virtual host isolation through Apache configuration, and disabling the mbstring.func_overload directive at the server level rather than allowing per-directory overrides. Security practitioners should also consider implementing monitoring for unauthorized .htaccess modifications and regularly audit server configurations to prevent such cross-site contamination. This vulnerability aligns with CWE-276, which addresses improper privilege management, and maps to ATT&CK technique T1548.001 for privilege escalation through configuration modifications. The remediation approach should emphasize proper access controls and configuration management practices that prevent local users from affecting system-wide settings that impact other hosted applications.