Mitigation of the Spring4Shell vulnerability: Overview and detection in 2022

A serious vulnerability in the Spring Java framework was revealed on March 29, 2022. This vulnerability was initially mistaken with CVE-2022-22963, a vulnerability in Spring Cloud. However, it was eventually discovered to be a different Spring Core vulnerability, now known as CVE-2022-22965 and dubbed Spring4Shell.

This vulnerability affects Spring Core and allows an attacker to overcome protections in the library’s HTTP request parser by sending a carefully crafted HTTP request, resulting in remote code execution. Several proofs of concept (PoCs) have been published, and active exploitation in the wild has been reported.

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Points to consider and observations

VMWare is notified of the Spring4Shell vulnerability on March 29, 2022. VMWare sends a message to the Spring team.

Spring launches its vulnerability response procedure on March 30, 2022. Spring claims that during this process, the vulnerability gets revealed to the public and various PoCs are released.

Spring posts a blog post on March 31, 2022, outlining the vulnerability, as well as remedial instructions and a schedule for the vulnerability disclosure process.

Because Spring is widely used in online applications, this vulnerability makes it an appealing target for threat actors looking to get access to unauthenticated remote code execution (RCE). Datadog has confirmed that this vulnerability is being actively exploited in the field.

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How does the Spring4Shell vulnerability work?

Image Courtesy: https://sysdig.com/

There are various proof-of-concepts for the Spring4Shell flaw already available. This GitHub repository has been forked or inspired by the majority of them.

The exploit is based on a carefully constructed HTTP request that takes advantage of Spring’s RequestMapping interface’s ability to interpret and parse web request query parameters. This interface links incoming web requests to the proper handling methods.

The RequestMapping interface’s filtering method for user-supplied data is where the Spring4Shell vulnerability is found. Spring4Shell-based attacks use Module.getClassLoader to deliver a payload (). An attacker can use this to load any malicious class that the server must parse. This attack route, which leads to the exploit, was not filtered in the vulnerable versions of Spring.

Check to see whether your app is vulnerable.

To be vulnerable to Spring4Shell, an application must meet many criteria mentioned in the Spring advisory:

• JDK 9 or above is recommended.
• As the servlet container, use Apache Tomcat.
• Assume the form of a conventional WAR (in contrast to a Spring Boot executable jar)
• Use the dependency spring-webmvc or spring-webflux.
• Use versions 5.3.0 to 5.3.17, 5.2.0 to 5.2.19, or older versions of the Spring framework.

Tools:

• https://github.com/redhuntlabs/Hunt4Spring
• https://github.com/onurgule/S4S-Scanner
• https://github.com/fracturelabs/go-scan-spring

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Guidance on Mitigation

VMWare has officially provided a confirmed patch for CVE-2022-22965, and we strongly advise that you update your software to Spring Framework 5.3.18. For Spring Framework 5.2.20, a backported fix is also available.

While these two updates solve the vulnerability, Spring Boot is still in the process of being released.

We recommend applying the confirmed fix instead of the interim patch that was released earlier today:

1:WAF Temporary Policy is the first temporary solution.

According on the actual traffic scenario of deployed services on network protection devices such as WAF, the

“class.*“，”Class.*“，”*.class.*“，”*.Class.*”

Add other string rules, and evaluate the business acceptable conditions after installing the filtering rules to avoid additional impact.

2. Mitigation measures for the time being

Create the following global class in the application system’s project package, and make sure it’s loaded by Spring (it is recommended to add it in the package where the Controller is located). After the class has been added, the project must be recompiled, packed, and functionally tested. and re-distribute the project.

import org.springframework.core.annotation.Order;

import org.springframework.web.bind.WebDataBinder;

import org.springframework.web.bind.annotation.ControllerAdvice;

import org.springframework.web.bind.annotation.InitBinder;

@ControllerAdvice

@Order(10000)

public class a{

@InitBinder

public void setAllowedFields(WebDataBinderdataBinder) {

String[] abd = new String[]{“class.*“, “Class.*“, “*.class.*“, “*.Class.*“};

dataBinder.setDisallowedFields(abd);

}}

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How Detox Can Assist?

Depending on application needs, VMWare recommends that affected clients upgrade to version 5.3.18 or higher, or version 5.2.20 or higher. The Spring Framework RCE, Early Announcement blog answer lists workarounds for users who are unable to update at this time.

Detox Technologies has experienced security specialists to swiftly and easily identify assets that are affected by the Spring4Shell vulnerability, remediate them, and track the issue.