CVE-2018-13818 in Twig
Summary
by MITRE
Twig before 2.4.4 allows Server-Side Template Injection (SSTI) via the search search_key parameter.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2018-13818 represents a critical server-side template injection flaw in the Twig template engine version 2.4.3 and earlier. This vulnerability specifically affects applications that utilize the search_key parameter within their template processing logic, creating a pathway for malicious actors to inject arbitrary template code that gets executed on the server. The issue stems from insufficient input validation and sanitization mechanisms within the template engine's handling of user-supplied parameters, particularly when these parameters are directly incorporated into template rendering processes without proper escaping or filtering.
The technical exploitation of this vulnerability occurs when an attacker can manipulate the search_key parameter to inject template syntax that gets processed by the Twig engine. This allows adversaries to execute arbitrary code on the server, potentially leading to complete system compromise. The vulnerability falls under CWE-94, which specifically addresses "Improper Control of Generation of Code ('Code Injection')" and aligns with ATT&CK technique T1059.002 for command and scripting interpreter. The flaw enables attackers to leverage the template engine's functionality to execute malicious payloads, often through the use of template syntax that can access system resources, make network requests, or execute shell commands depending on the application's configuration and the underlying server environment.
The operational impact of CVE-2018-13818 extends beyond simple code execution to encompass full system compromise and data exfiltration capabilities. Organizations using vulnerable versions of Twig are at risk of unauthorized access, data breaches, and potential lateral movement within their networks. The vulnerability is particularly dangerous because it can be exploited through seemingly benign search functionality, making it difficult to detect and mitigate. Attackers can leverage this flaw to establish persistent access, escalate privileges, or use the compromised system as a launching point for further attacks against other network resources. The server-side nature of the vulnerability means that the attack vector operates entirely on the backend, potentially bypassing client-side security controls and network segmentation measures.
Mitigation strategies for CVE-2018-13818 primarily focus on upgrading to Twig version 2.4.4 or later, which includes proper input sanitization and validation mechanisms. Organizations should also implement comprehensive input validation at multiple layers, including application-level filtering and escaping of user-supplied parameters before they are processed by the template engine. Security measures should include the implementation of web application firewalls that can detect and block suspicious template injection patterns, along with regular security testing and code reviews to identify potential template injection vulnerabilities. Additionally, organizations should consider implementing strict template sandboxing policies that limit the capabilities available to template rendering engines, particularly when processing untrusted input. The remediation process should also include monitoring for anomalous template processing behavior and establishing incident response procedures specifically designed to address template injection attacks. Organizations must also ensure that their security awareness training includes recognition of potential template injection attack vectors, particularly in search and filtering functionality where such vulnerabilities commonly occur.