CVE-2016-4465 in Struts
Summary
by MITRE
The URLValidator class in Apache Struts 2 2.3.20 through 2.3.28.1 and 2.5.x before 2.5.1 allows remote attackers to cause a denial of service via a null value for a URL field.
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Analysis
by VulDB Data Team • 02/16/2019
The vulnerability identified as CVE-2016-4465 resides within the URLValidator class of Apache Struts 2 framework, affecting versions ranging from 2.3.20 through 2.3.28.1 and all 2.5.x versions prior to 2.5.1. This issue represents a critical denial of service vulnerability that can be exploited by remote attackers to disrupt the normal operation of applications built on this framework. The flaw manifests when the URLValidator processes a URL field containing a null value, creating a scenario where the application's validation logic fails catastrophically. The vulnerability falls under the category of improper input validation as defined by CWE-20, where the system fails to properly validate or sanitize input data before processing it. This weakness enables attackers to craft malicious requests that trigger unexpected behavior in the application's validation layer.
The technical exploitation of this vulnerability occurs when an attacker submits a request containing a null value for a URL field that is expected to be validated by the URLValidator. The validator class does not adequately handle null inputs, leading to a NullPointerException or similar runtime exception that causes the application to crash or become unresponsive. This type of vulnerability is particularly dangerous in web applications because it can be triggered through simple HTTP requests without requiring authentication or advanced exploitation techniques. The vulnerability directly impacts the availability aspect of the application's security posture, as successful exploitation results in denial of service conditions that can render the application inaccessible to legitimate users. The flaw demonstrates poor error handling practices and insufficient null value checking within the validation logic, which is a fundamental security principle that should be enforced across all input processing components.
From an operational perspective, this vulnerability poses significant risks to organizations relying on Apache Struts 2 applications, as it can be exploited to cause widespread service disruption without requiring sophisticated attack vectors. The impact extends beyond simple application crashes to potentially affect business continuity and customer experience, especially in mission-critical applications where availability is paramount. The vulnerability aligns with attack patterns documented in the MITRE ATT&CK framework under the service stoppage category, where adversaries target system availability through resource exhaustion or application instability. Organizations may experience cascading effects from such an attack, as the denial of service can impact dependent systems, trigger alerting mechanisms, and require immediate incident response activities. The exploitation of this vulnerability can be automated and scaled, making it particularly dangerous in environments where applications are exposed to untrusted network traffic.
Mitigation strategies for CVE-2016-4465 primarily involve upgrading to patched versions of Apache Struts 2 framework, specifically versions 2.3.29 or 2.5.1 and later, which contain the necessary fixes to properly handle null values in URL validation. Organizations should implement comprehensive patch management processes to ensure all affected systems are updated promptly. Additionally, implementing input validation at multiple layers of the application architecture can provide defense in depth, including validating URL fields before they reach the URLValidator component. Network-level mitigations such as web application firewalls can help detect and block malicious requests attempting to exploit this vulnerability. Security monitoring should be enhanced to detect unusual patterns of service disruption or application instability that may indicate exploitation attempts. The vulnerability underscores the importance of thorough testing of validation logic, particularly around edge cases involving null or empty values, and emphasizes the need for robust error handling throughout application components. Regular security assessments and code reviews focused on input validation routines should be conducted to identify similar weaknesses in other components of the application stack.