CVE-2013-6501 in PHP
Summary
by MITRE
The default soap.wsdl_cache_dir setting in (1) php.ini-production and (2) php.ini-development in PHP through 5.6.7 specifies the /tmp directory, which makes it easier for local users to conduct WSDL injection attacks by creating a file under /tmp with a predictable filename that is used by the get_sdl function in ext/soap/php_sdl.c.
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Analysis
by VulDB Data Team • 03/10/2022
The vulnerability identified as CVE-2013-6501 represents a critical security flaw in PHP versions through 5.6.7 that stems from improper default configuration settings in the SOAP extension. This issue specifically affects the soap.wsdl_cache_dir parameter which is configured to point to the /tmp directory in both php.ini-production and php.ini-development configuration files. The fundamental problem arises from the predictable nature of the /tmp directory structure and the lack of proper file permissions that allows local attackers to manipulate the WSDL caching mechanism. When PHP processes WSDL files through the SOAP extension, it stores cached versions in the designated cache directory, and the predictable filename generation creates opportunities for attackers to pre-position malicious files before the legitimate WSDL processing occurs.
The technical implementation of this vulnerability occurs within the ext/soap/php_sdl.c source file where the get_sdl function handles WSDL file processing and caching operations. This function generates cache filenames based on predictable patterns that can be easily guessed or reproduced by local users. When an attacker creates a malicious file with a specific filename in the /tmp directory before the legitimate WSDL processing occurs, the SOAP extension will use the attacker-controlled file instead of the intended WSDL file. This creates a classic race condition scenario where the attacker can inject malicious content that gets executed during SOAP processing operations, effectively bypassing normal security controls and authentication mechanisms.
The operational impact of this vulnerability extends beyond simple local privilege escalation to encompass broader security implications for web applications that utilize SOAP services. Attackers can leverage this weakness to inject malicious WSDL files that contain harmful code or manipulate existing WSDL structures to redirect service calls to attacker-controlled endpoints. This opens the door to various attack vectors including data exfiltration, service disruption, and potentially remote code execution depending on how the SOAP service is implemented and configured. The vulnerability is particularly dangerous in shared hosting environments or multi-tenant systems where multiple users have access to the same /tmp directory space, as it allows one user to affect the operations of other users running SOAP-based applications.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-352 (Cross-Site Request Forgery) and CWE-22 (Path Traversal) categories, representing a combination of configuration weakness and privilege escalation risks. The ATT&CK framework categorizes this under T1059 (Command and Scripting Interpreter) and T1068 (Exploitation for Privilege Escalation) techniques, as attackers can leverage the WSDL injection to execute arbitrary code with the privileges of the web server process. The vulnerability also demonstrates poor security by design principles where default configurations do not consider the security implications of placing cache files in world-writable directories like /tmp, violating the principle of least privilege and secure configuration management.
Mitigation strategies for CVE-2013-6501 should focus on both immediate configuration changes and long-term architectural improvements. Organizations should immediately modify the soap.wsdl_cache_dir parameter to point to a secure, non-world-writable directory with appropriate permissions and access controls. The recommended approach involves creating a dedicated cache directory with restrictive permissions such as 700 or 750, ensuring that only the web server process can read and write to this location. Additionally, implementing proper file system permissions and using tools like SELinux or AppArmor can provide additional layers of protection. The PHP development team addressed this issue by changing the default configuration in later releases, emphasizing the importance of secure default settings and proper security hardening practices. Organizations should also implement monitoring and alerting for unusual file creation patterns in cache directories and regularly audit their PHP configurations to ensure compliance with security best practices.