CVE-2015-7809 in TWIG
Summary
by MITRE
The displayBlock function Template.php in Sensio Labs Twig before 1.20.0, when Sandbox mode is enabled, allows remote attackers to execute arbitrary code via the _self variable in a template.
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Analysis
by VulDB Data Team • 06/26/2022
The vulnerability identified as CVE-2015-7809 represents a critical code execution flaw within the Sensio Labs Twig templating engine prior to version 1.20.0. This issue specifically manifests when the sandbox mode is enabled, creating a dangerous condition where remote attackers can manipulate template variables to achieve unauthorized code execution on affected systems. The vulnerability resides within the displayBlock function located in the Template.php file, which serves as a core component of Twig's template processing architecture. When sandbox mode is active, the system should restrict template execution to prevent access to potentially harmful operations, but this protection mechanism fails to adequately validate the _self variable, allowing attackers to bypass these security controls.
The technical exploitation of this vulnerability stems from the improper handling of the _self variable within the sandbox environment. In Twig's templating system, the _self variable typically refers to the current template object, but when sandbox mode is enabled, this variable should be restricted to prevent access to underlying PHP functions and system operations. Attackers can manipulate this variable to inject malicious code that gets executed within the template context, effectively circumventing the sandbox protections designed to isolate template execution from the underlying system. This flaw directly relates to CWE-94, which describes "Improper Control of Generation of Code ('Code Injection')" and represents a classic example of how insufficient input validation can lead to arbitrary code execution vulnerabilities.
The operational impact of CVE-2015-7809 extends beyond simple code execution, as it can enable attackers to gain full control over affected systems running vulnerable versions of Twig. Since Twig is widely used in web applications, content management systems, and various PHP-based platforms, the potential attack surface is extensive. An attacker who successfully exploits this vulnerability can execute arbitrary commands, access sensitive data, modify application behavior, and potentially establish persistent access to compromised systems. This vulnerability particularly affects web applications that utilize Twig templating with sandbox mode enabled, making it a significant concern for organizations relying on these frameworks for their web applications.
Mitigation strategies for CVE-2015-7809 primarily involve upgrading to Twig version 1.20.0 or later, which includes proper validation of the _self variable within sandbox mode. Organizations should also implement additional security measures such as restricting template compilation permissions, monitoring for unusual template execution patterns, and conducting regular security assessments of their templating systems. The remediation process should include thorough testing of the updated Twig version to ensure that existing functionality remains intact while the security vulnerability is resolved. Security teams should also consider implementing web application firewalls and runtime application self-protection mechanisms as additional layers of defense against similar vulnerabilities. This vulnerability demonstrates the critical importance of proper sandbox implementation and input validation in preventing code injection attacks, aligning with ATT&CK techniques that focus on code injection and privilege escalation within application environments.