In this long-read post, we will take a deep dive into CVE-2024-38808, a vulnerability found in the Spring Framework, specifically affecting versions 5.3. through 5.3.38 and older unsupported versions. The vulnerability, related to the evaluation of malicious Spring Expression Language (SpEL) expressions, can lead to a denial of service (DoS) condition. We will provide code snippets, links to original references, and exploit details to better understand this issue and its implications.

Vulnerability details

The Spring Framework, a popular Java-based application framework, contains a vulnerability in its implementation of processing user-supplied SpEL expressions. An attacker can exploit this vulnerability by crafting a malicious SpEL expression that, when evaluated by the vulnerable application, causes a DoS condition.

An application is specifically vulnerable when it meets the following conditions

* The application evaluates user-supplied SpEL expressions.

Exploit details

An attacker can craft a SpEL expression that causes the application to consume excessive resources, such as CPU time or memory, ultimately leading to a DoS condition. This type of attack is known as an algorithmic complexity attack that targets the evaluation mechanism of SpEL expressions.

For example, suppose an application contains the following code snippet, which evaluates a user-supplied SpEL expression:

import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;

public class VulnerableSpringApp {
    public static void main(String[] args) {
        ExpressionParser parser = new SpelExpressionParser();
        String userInput = args[];
        System.out.println(parser.parseExpression(userInput).getValue());
    }
}

An attacker may provide a specially crafted SpEL expression like the following

T(java.lang.String).valueOf(new int[100000]).substring(new int[100000], new int[100000])

This SpEL expression would cause the application to create and process large amounts of data, potentially leading to significant resource consumption and eventual DoS condition.

Mitigation and recommendations

Developers using the Spring Framework should ensure that their applications do not evaluate untrusted user-supplied SpEL expressions. If this is unavoidable, it is recommended that developers implement proper input validation and rate-limiting mechanisms to minimize the risk of DoS attacks.

The Spring Framework team has released patches addressing this vulnerability. Users of affected versions are strongly encouraged to upgrade to a newer, fixed version as soon as possible.

For versions in the 5.3.x branch, upgrading to version 5.3.39 or newer should address the issue

- Spring Framework 5.3.39

For users running older unsupported versions, it is recommended to upgrade to a supported version to receive important security updates and fixes.

Further references and information

- CVE-2024-38808 - Mitre CVE Page
- Spring Framework Release Notes - Details on security fixes and updates
- Spring Security Expression Language Guide - Recommendations for securing SpEL in Spring Security

Conclusion

CVE-2024-38808 is a critical vulnerability in the Spring Framework that can lead to DoS conditions when an attacker provides malicious SpEL expressions. Developers should be cautious of evaluating untrusted user input and should upgrade their Spring Framework versions to protect their applications.

Timeline

Published on: 08/20/2024 08:15:05 UTC
Last modified on: 08/20/2024 15:44:20 UTC