CVE-2008-4811 in Smarty
Summary
by MITRE
The _expand_quoted_text function in libs/Smarty_Compiler.class.php in Smarty 2.6.20 r2797 and earlier allows remote attackers to execute arbitrary PHP code via vectors related to templates and a \ (backslash) before a dollar-sign character.
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Analysis
by VulDB Data Team • 08/20/2019
The vulnerability identified as CVE-2008-4811 represents a critical remote code execution flaw within the Smarty template engine version 2.6.20 and earlier releases. This vulnerability exists in the _expand_quoted_text function located within the libs/Smarty_Compiler.class.php file, which serves as the core compilation component responsible for processing template files. The flaw specifically manifests when the template parser encounters a backslash character immediately preceding a dollar-sign character within template content, creating a dangerous condition that can be exploited by remote attackers to execute arbitrary PHP code on the affected system.
The technical nature of this vulnerability stems from improper input validation and sanitization within the template compilation process. When Smarty processes templates containing maliciously crafted sequences with backslash followed by dollar-sign characters, the _expand_quoted_text function fails to properly escape or validate these sequences, allowing attackers to inject arbitrary PHP code that gets executed during template compilation. This represents a classic case of insecure template processing where user-supplied template data is not adequately sanitized before being compiled into executable PHP code. The vulnerability operates at the parser level within the template engine, making it particularly dangerous as it can be triggered through any template processing mechanism that utilizes the affected function.
The operational impact of this vulnerability is severe and far-reaching, as it enables remote attackers to achieve complete system compromise without requiring authentication or specific privileges. An attacker can craft malicious templates that, when processed by the vulnerable Smarty version, will execute arbitrary PHP code with the privileges of the web server process. This can lead to complete system takeover, data exfiltration, lateral movement within network environments, and persistent backdoor installation. The vulnerability affects any web application using Smarty 2.6.20 or earlier that accepts user input for template processing, making it particularly dangerous in content management systems, web applications, and any platform relying on Smarty for template rendering. The impact extends beyond immediate code execution to include potential privilege escalation, system reconnaissance, and data breach capabilities.
Organizations affected by this vulnerability should immediately implement multiple layers of mitigation strategies to protect their systems. The primary and most effective mitigation involves upgrading to Smarty version 2.6.21 or later, which contains the necessary patches to address the template parsing flaw. Additionally, administrators should implement strict input validation and sanitization for all template content, particularly when accepting user-generated templates or template fragments. Web application firewalls can be configured to detect and block suspicious template patterns containing backslash-dollar sequences. Input filtering should be implemented at multiple levels including application code, web server configurations, and database layer to prevent malicious template data from reaching the Smarty compiler. The vulnerability aligns with CWE-94, which describes "Improper Control of Generation of Code ('Code Injection')" and can be mapped to ATT&CK technique T1190, "Exploit Public-Facing Application," as it represents a remote code execution vulnerability in widely used web application components. System hardening measures including reduced file permissions for template directories and implementation of proper access controls should also be enforced to minimize potential damage from successful exploitation attempts.