CVE-2005-0913 in Smarty
Summary
by MITRE
Unknown vulnerability in the regex_replace modifier (modifier.regex_replace.php) in Smarty before 2.6.8 allows attackers to execute arbitrary PHP code.
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Analysis
by VulDB Data Team • 07/01/2021
The vulnerability identified as CVE-2005-0913 represents a critical security flaw in the Smarty template engine, specifically within the regex_replace modifier functionality. This issue affects Smarty versions prior to 2.6.8 and stems from inadequate input validation and sanitization mechanisms within the modifier.regex_replace.php file. The flaw enables remote attackers to inject malicious PHP code through crafted input that gets processed by the regex_replace function, potentially leading to complete system compromise. The vulnerability operates at the intersection of template processing and code execution, making it particularly dangerous in web applications that utilize Smarty for dynamic content generation and user input handling.
The technical implementation of this vulnerability exploits the way Smarty handles regular expression replacement operations within template files. When the regex_replace modifier processes user-supplied data, it fails to properly sanitize or escape special regex metacharacters that could contain PHP code injection payloads. This allows attackers to manipulate the regular expression pattern parameter in such a way that it executes arbitrary PHP code during template compilation or rendering. The flaw essentially creates a code execution pathway through the template engine's modifier system, bypassing normal input validation controls that should prevent such malicious code injection. The vulnerability aligns with CWE-94, which categorizes improper control of generation of code, and represents a classic example of code injection vulnerability within template processing frameworks.
The operational impact of CVE-2005-0913 extends beyond simple code execution to encompass full system compromise capabilities. Attackers can leverage this vulnerability to execute arbitrary commands on the web server, potentially gaining access to sensitive data, modifying application behavior, or establishing persistent backdoors. The vulnerability affects web applications that rely on Smarty template processing for dynamic content generation, making it particularly dangerous in content management systems, web applications, and any platform that accepts user input through templates. The risk is amplified when applications do not implement proper input validation or when administrators fail to keep Smarty updated to patched versions. This vulnerability directly maps to ATT&CK technique T1059.006, which covers the execution of code through web shells or similar mechanisms, and represents a common attack vector in web application exploitation.
Organizations affected by this vulnerability should immediately implement comprehensive mitigation strategies focusing on both immediate remediation and long-term security hardening. The primary and most effective mitigation involves upgrading to Smarty version 2.6.8 or later, which includes proper input sanitization and validation for the regex_replace modifier. Additionally, administrators should implement strict input validation at multiple layers, including application-level filtering and regular expression escaping for all user-supplied data processed through template engines. Network-based mitigations such as web application firewalls can provide additional protection by detecting and blocking suspicious regex patterns, though these should not be considered replacements for proper code updates. The vulnerability underscores the importance of maintaining current software versions and implementing robust security practices around template processing, particularly in frameworks that handle user-generated content. Organizations should also conduct thorough security audits of their template usage patterns to identify other potential injection points and ensure proper security controls are in place to prevent similar vulnerabilities from being exploited in other parts of their web applications.