CVE-2021-46433 in fenom
Summary
by MITRE • 03/28/2022
In fenom 2.12.1 and before, there is a way in fenom/src/Fenom/Template.php function getTemplateCode()to bypass sandbox to execute arbitrary PHP code when disable_native_funcs is true.
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Analysis
by VulDB Data Team • 03/31/2022
The vulnerability identified as CVE-2021-46433 affects the fenom template engine version 2.12.1 and earlier, representing a critical sandbox bypass issue that allows arbitrary PHP code execution. This flaw exists within the getTemplateCode() function located in fenom/src/Fenom/Template.php, where the security mechanisms designed to prevent code execution are circumvented even when the disable_native_funcs configuration parameter is set to true. The vulnerability fundamentally undermines the intended security model of the template engine by allowing attackers to execute malicious PHP code through carefully crafted template inputs.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the template processing pipeline. When disable_native_funcs is enabled as a security measure, it typically restricts the execution of native PHP functions that could pose security risks. However, the flaw in getTemplateCode() function allows attackers to bypass these restrictions through specific template syntax manipulation that leverages the template engine's internal processing mechanisms. This bypass occurs at the parsing and code generation level where the engine translates template code into executable PHP, creating a path for malicious code injection that circumvents the intended security boundaries.
The operational impact of this vulnerability is severe and far-reaching, as it provides attackers with complete arbitrary code execution capabilities on systems running vulnerable versions of the fenom template engine. This vulnerability can be exploited in web applications that utilize fenom for template processing, potentially allowing attackers to escalate privileges, access sensitive data, modify application behavior, or establish persistent access to affected systems. The vulnerability is particularly dangerous because it can be exploited without requiring elevated privileges or specific system access, making it a high-value target for attackers seeking to compromise web applications. The bypass of the disable_native_funcs setting means that even organizations that have implemented this security measure as a defense-in-depth strategy may still be vulnerable to exploitation.
Organizations should immediately update to fenom versions 2.12.2 or later, which contain patches addressing this specific vulnerability. Additionally, implementing proper input validation and sanitization measures, monitoring for suspicious template code patterns, and conducting regular security assessments of template processing components can help mitigate the risk. The vulnerability aligns with CWE-94, which covers "Improper Control of Generation of Code ('Code Injection')" and relates to ATT&CK technique T1059.007 for "Command and Scripting Interpreter: Python" where similar bypass mechanisms can be exploited. Security teams should also consider implementing web application firewalls and runtime application self-protection mechanisms to detect and prevent exploitation attempts. Regular security training for developers on secure template processing practices and code review procedures can further reduce the attack surface and prevent similar vulnerabilities from being introduced in the future.