CVE-2011-3379 in PHP
Summary
by MITRE
The is_a function in PHP 5.3.7 and 5.3.8 triggers a call to the __autoload function, which makes it easier for remote attackers to execute arbitrary code by providing a crafted URL and leveraging potentially unsafe behavior in certain PEAR packages and custom autoloaders.
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Analysis
by VulDB Data Team • 11/25/2021
The vulnerability identified as CVE-2011-3379 represents a critical security flaw in PHP versions 5.3.7 and 5.3.8 that exploits the interaction between the is_a function and the __autoload mechanism. This vulnerability falls under the category of improper input validation and unsafe autoload behavior, creating a dangerous condition where remote attackers can manipulate object type checking operations to execute arbitrary code. The flaw specifically manifests when the is_a function is called with a maliciously crafted class name parameter that triggers the __autoload function, which then executes arbitrary code through potentially unsafe autoloaders or PEAR package behaviors.
The technical implementation of this vulnerability leverages PHP's dynamic class loading mechanism where the is_a function internally calls __autoload when checking if an object is an instance of a particular class. When an attacker provides a crafted class name that triggers __autoload, the function can be manipulated to load malicious code from remote sources or local files that are not properly validated. This creates a path where attackers can inject code through the autoload process, particularly when PEAR packages or custom autoloaders contain unsafe behavior or lack proper input sanitization. The vulnerability is classified under CWE-94 as "Improper Control of Generation of Code ('Code Injection')" and aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: PowerShell" and T1059.006 for "Command and Scripting Interpreter: Python" when considering the broader category of code execution through dynamic loading mechanisms.
The operational impact of CVE-2011-3379 is severe as it allows remote code execution without requiring authentication, making it particularly dangerous for web applications that use PHP and rely on dynamic class loading. Attackers can exploit this vulnerability by constructing a malicious URL that triggers the is_a function with crafted parameters, potentially leading to complete system compromise. The vulnerability is especially concerning in environments where PEAR packages are used, as many of these packages may not properly validate class names or may contain unsafe autoload behaviors that can be exploited through this mechanism. The exploitation requires minimal privileges and can be automated, making it a preferred target for automated attack tools and script kiddies.
Mitigation strategies for CVE-2011-3379 primarily focus on immediate patching of affected PHP versions to 5.3.9 or later, where the vulnerability has been resolved through proper input validation in the is_a function implementation. Organizations should also implement strict input validation for all class name parameters and avoid using potentially unsafe autoloaders that do not properly sanitize input. The use of PHP's built-in error handling and the implementation of proper security measures such as disabling dangerous functions, using secure coding practices, and implementing proper access controls can significantly reduce the risk of exploitation. Additionally, network segmentation, web application firewalls, and regular security audits can provide additional layers of protection against this type of vulnerability, while monitoring for unusual patterns in class loading operations can help detect potential exploitation attempts.