CVE-2016-4465: DoS attack vulnerability in Apache Struts 2 URLValidator

Background

Apache Struts 2 is an open-source framework for developing Java web applications. It provides a set of tools and libraries to simplify the development process and enhance the security of web applications. The URLValidator class in Apache Struts 2 is responsible for validating URLs provided as input. However, versions 2.3.20 through 2.3.28.1 and 2.5.x before 2.5.1 are vulnerable to a denial of service (DoS) attack when a null value is passed for a URL field. This vulnerability can be exploited remotely by attackers to disrupt the normal functioning of the application.

Vulnerability Detail

The vulnerability (CVE-2016-4465) in Apache Struts 2 allows remote attackers to cause a denial of service (DoS) by providing a null value for a URL field. When the URLValidator class encounters a null value, it fails to handle it properly, leading to a DoS condition. This vulnerability can be exploited remotely, without requiring any authentication or user interaction. The impact of this vulnerability is a disruption of the affected application's availability, potentially leading to financial losses or reputational damage. The Common Vulnerability Scoring System (CVSS) score for this vulnerability is 5.3, indicating a moderate severity level.

Workaround

As a temporary workaround, developers can manually validate URL fields before passing them to the URLValidator class. This can be done by checking for null values and ensuring that a valid URL is provided. Here is an example of how to perform this validation in Java:

String url = ...; // URL input

if (url != null && !url.isEmpty()) {
    // Perform URL validation
    URLValidator validator = new URLValidator();
    boolean isValid = validator.isValid(url);
    // Further processing
}

By explicitly checking for null values and validating the URL separately, developers can mitigate the risk of a DoS attack.

Conclusion

In conclusion, the Apache Struts 2 URLValidator vulnerability (CVE-2016-4465) allows remote attackers to cause a denial of service (DoS) by providing a null value for a URL field. This vulnerability can be mitigated by upgrading to the fixed versions of Apache Struts 2 or by implementing a temporary workaround. For further assistance or support in addressing this vulnerability, please contact DevNack.com.

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