CVE-2018-18893 in Goldengate
Summary
by MITRE
Jinjava before 2.4.6 does not block the getClass method, related to com/hubspot/jinjava/el/ext/JinjavaBeanELResolver.java.
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Analysis
by VulDB Data Team • 11/10/2022
The vulnerability identified as CVE-2018-18893 affects the Jinjava template engine version 2.4.5 and earlier, representing a critical security flaw in the expression language evaluation component. This issue stems from insufficient method filtering within the JinjavaBeanELResolver.java class, which is responsible for resolving bean properties during template execution. The vulnerability specifically allows attackers to bypass security restrictions by accessing the getClass method through template expressions, thereby undermining the sandboxed execution environment that Jinjava is designed to provide.
The technical flaw manifests in the improper handling of method resolution within the expression language parser, where the getClass method remains accessible despite being explicitly blocked in the security configuration. This occurs because the JinjavaBeanELResolver.java implementation fails to adequately filter out potentially dangerous methods that could enable object introspection and class loading operations. Attackers can leverage this vulnerability to execute arbitrary code by constructing malicious template expressions that invoke getClass and subsequently access class loading mechanisms through the Java reflection API. The vulnerability directly maps to CWE-470, which addresses the use of insecure deserialization and unsafe reflection operations in software systems.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to gain unauthorized access to the underlying Java runtime environment. Through the getClass method, malicious actors can traverse object hierarchies and potentially access sensitive system resources, including file systems, network connections, and memory structures. This capability significantly increases the attack surface for applications using Jinjava templates, particularly those that process untrusted user input through template rendering. The vulnerability is particularly dangerous in web applications where user-generated content is processed through Jinjava templates, as it allows for remote code execution and complete system compromise.
Mitigation strategies for CVE-2018-18893 require immediate patching of affected Jinjava versions to 2.4.6 or later, which includes proper method filtering in the expression language resolver. Organizations should also implement comprehensive input validation and sanitization practices, ensuring that all user-supplied template content undergoes rigorous security screening before processing. Additionally, security teams should consider implementing runtime monitoring and anomaly detection systems to identify potential exploitation attempts. The vulnerability demonstrates the importance of proper sandboxing mechanisms in template engines and aligns with ATT&CK technique T1059.007 for application layer execution. Organizations should also review their template security configurations and ensure that all potentially dangerous methods are properly restricted, following the principle of least privilege in expression language evaluation.