CVE-2016-4438 in Struts
Summary
by MITRE
The REST plugin in Apache Struts 2 2.3.20 through 2.3.28.1 allows remote attackers to execute arbitrary code via a crafted expression.
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Analysis
by VulDB Data Team • 02/16/2019
The vulnerability identified as CVE-2016-4438 represents a critical remote code execution flaw within the REST plugin of Apache Struts 2 framework. This vulnerability affects versions ranging from 2.3.20 through 2.3.28.1, making it a significant concern for organizations utilizing this web application framework. The issue stems from inadequate input validation and sanitization mechanisms within the plugin's expression processing capabilities, creating a pathway for malicious actors to inject and execute arbitrary code on affected systems. The vulnerability operates through the manipulation of expression language constructs that are processed by the framework's internal evaluation engine, allowing attackers to leverage the system's processing capabilities for unauthorized operations.
The technical flaw manifests in the improper handling of user-supplied input within the REST plugin's expression evaluation system. When the framework processes requests containing crafted expressions, it fails to adequately sanitize or validate the input before executing the associated code. This weakness falls under the category of expression language injection vulnerabilities, which are categorized as CWE-94 in the Common Weakness Enumeration system. The vulnerability specifically targets the framework's ability to process OGNL (Object-Graph Navigation Language) expressions, which are used extensively within Struts 2 for data binding and expression evaluation. Attackers can construct malicious expressions that, when processed by the vulnerable plugin, result in arbitrary code execution on the server hosting the application.
The operational impact of this vulnerability extends far beyond simple data compromise, as successful exploitation allows attackers to gain complete control over affected systems. Organizations running vulnerable Struts 2 applications face significant risks including data theft, system infiltration, lateral movement within network environments, and potential establishment of persistent backdoors. The remote nature of the attack means that threat actors can exploit this vulnerability from anywhere on the internet without requiring physical access or prior authentication. This makes the vulnerability particularly dangerous as it can be exploited by automated scanning tools, leading to widespread compromise of systems that are not properly monitored or patched. The vulnerability also enables attackers to perform reconnaissance activities, escalate privileges, and potentially compromise other systems within the same network infrastructure.
Mitigation strategies for CVE-2016-4438 primarily focus on immediate patching of affected systems, with Apache Struts 2 versions 2.3.29 and later recommended for deployment. Organizations should implement comprehensive input validation mechanisms and restrict the use of expression language constructs where possible. Network segmentation and firewall rules should be configured to limit access to affected applications, while intrusion detection systems should be enhanced to monitor for suspicious expression language patterns. Security teams should also conduct thorough vulnerability assessments to identify all instances of the affected plugin and ensure complete remediation. The ATT&CK framework categorizes this vulnerability under the T1059.001 technique for Command and Scripting Interpreter, highlighting the execution of malicious code through the framework's expression evaluation capabilities. Additionally, organizations should implement application firewalls and Web Application Firewalls to filter out malicious requests before they reach the vulnerable plugin components. Regular security audits and penetration testing should be conducted to verify that all instances of the vulnerable plugin have been properly addressed and that no legacy systems remain exposed to this critical vulnerability.