CVE-2012-1171 in PHP
Summary
by MITRE
The libxml RSHUTDOWN function in PHP 5.x allows remote attackers to bypass the open_basedir protection mechanism and read arbitrary files via vectors involving a stream_close method call during use of a custom stream wrapper.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 03/11/2022
The vulnerability identified as CVE-2012-1171 represents a critical security flaw in PHP's libxml extension that undermines fundamental access control mechanisms. This issue specifically targets the RSHUTDOWN function within the libxml component of PHP 5.x versions, creating a pathway for remote attackers to circumvent the open_basedir directive. The open_basedir protection mechanism serves as a crucial security boundary that restricts PHP scripts from accessing files outside of designated directories, making this bypass particularly dangerous for web applications that rely on such restrictions for data protection. The vulnerability operates through a sophisticated attack vector that leverages the stream_close method call within custom stream wrapper implementations, effectively allowing malicious actors to read arbitrary files on the server.
The technical exploitation of this vulnerability occurs when PHP processes XML data through libxml functions while custom stream wrappers are active. During the shutdown phase of the libxml extension, the RSHUTDOWN function executes stream_close method calls that fail to properly validate file access permissions. This flaw enables attackers to manipulate the stream wrapper behavior to access files outside of the configured open_basedir restrictions, effectively nullifying the intended security boundaries. The attack requires the presence of a custom stream wrapper that can be manipulated during the XML processing lifecycle, making the vulnerability particularly insidious as it exploits legitimate PHP functionality rather than introducing new attack vectors. The flaw essentially creates a race condition or improper state management during the stream cleanup process where file access controls are bypassed.
The operational impact of CVE-2012-1171 extends beyond simple file access violations, as it can lead to complete system compromise when combined with other vulnerabilities or when attackers have knowledge of the underlying file structure. This vulnerability allows for information disclosure attacks where attackers can read sensitive files such as configuration files, database credentials, application source code, and system files that should remain protected. The implications are particularly severe in shared hosting environments or multi-tenant applications where proper isolation between different user accounts is essential. Security professionals should recognize this vulnerability as a potential entry point for more extensive attacks, including privilege escalation, data exfiltration, and system reconnaissance. The vulnerability also demonstrates poor adherence to security principles outlined in the CWE catalog under CWE-284, which addresses improper access control mechanisms, and aligns with ATT&CK techniques focused on privilege escalation and credential access through software exploitation.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to PHP versions that contain the patched libxml extension, disabling unnecessary stream wrappers, and implementing additional access controls beyond the open_basedir directive. The recommended approach involves applying the official PHP security patches that address the improper stream handling during the RSHUTDOWN phase and ensuring that all custom stream wrappers properly validate file access permissions. Security monitoring should focus on detecting unusual XML processing activities and unauthorized file access patterns. Additionally, administrators should consider implementing web application firewalls and runtime application self-protection mechanisms to detect and prevent exploitation attempts. The vulnerability serves as a reminder of the importance of proper resource management and access control validation in extension modules, particularly when dealing with file system operations during application shutdown phases. This issue underscores the critical need for comprehensive security testing of PHP extensions and the implementation of defense-in-depth strategies that provide multiple layers of protection against similar vulnerabilities.