CVE-2021-3690 High Severity Vulnerability In Undertow-core-2.2.16.Final.jar Analysis And Mitigation

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Understanding the CVE-2021-3690 Vulnerability

This article delves into the high-severity vulnerability CVE-2021-3690 that affects the undertow-core-2.2.16.Final.jar library. This vulnerability, identified in the Undertow web server, can lead to a denial-of-service (DoS) attack. Understanding the intricacies of this vulnerability is crucial for developers and security professionals to mitigate potential risks and ensure the security of their applications.

Vulnerable Library Details: undertow-core-2.2.16.Final.jar

The vulnerable component is the undertow-core-2.2.16.Final.jar library, a core part of the Undertow web server. Undertow is a flexible and high-performance web server written in Java, often used in applications requiring robust web capabilities. The library's home page can be found at http://www.jboss.org. In the context of this vulnerability, the library is flagged within the WebGoat8/pom.xml file, indicating its presence in the WebGoat8 project, a deliberately vulnerable web application used for security training and testing.

Dependency Hierarchy and Vulnerability Location

The vulnerability is present in the dependency hierarchy of spring-boot-starter-undertow-2.6.6.jar, which includes the vulnerable undertow-core-2.2.16.Final.jar. This means that applications using the Spring Boot Undertow starter are potentially at risk. The specific commit where this vulnerability is identified is 0be5be44b8f7821af77da18ba5c032b48d43bf91 in the SAST-Test-Repo-03c74fb5-dd3d-465e-b184-3d7fb4ea05d0 repository. The vulnerability is also present in the main branch of the repository, highlighting its persistence across the codebase.

Deep Dive into the Vulnerability Details

The core issue behind CVE-2021-3690 is a buffer leak that occurs during the processing of incoming WebSocket PONG messages. Specifically, the flaw allows for a memory exhaustion scenario, which can be triggered by an attacker sending malicious or excessive PONG messages. This memory exhaustion ultimately leads to a denial-of-service condition, making the affected application or server unavailable to legitimate users. The highest threat associated with this vulnerability is availability, as it directly impacts the system's ability to serve requests.

Technical Explanation of the Buffer Leak

To understand the vulnerability fully, it's essential to grasp the underlying technical details. A buffer leak occurs when a program allocates memory for a specific operation but fails to release it after the operation is complete. In the case of CVE-2021-3690, the Undertow server, when handling WebSocket PONG messages, does not properly manage the memory allocated for these messages. Over time, if an attacker floods the server with PONG messages, the unreleased memory accumulates, eventually exhausting the available memory resources. This memory exhaustion causes the server to slow down significantly or crash altogether, resulting in a denial-of-service.

Impact of the Denial-of-Service (DoS)

The impact of a denial-of-service attack can be significant, especially for critical applications. A DoS attack can disrupt business operations, damage reputation, and lead to financial losses. In scenarios where applications provide essential services, such as e-commerce platforms, healthcare systems, or financial services, a DoS attack can have severe consequences. Therefore, addressing vulnerabilities like CVE-2021-3690 is crucial for maintaining system reliability and ensuring business continuity.

Mend Note and Public Disclosure

The vulnerability was publicly disclosed on August 23, 2022, as per the Mend vulnerability database. The CVE entry provides essential information about the vulnerability, including its description, affected components, and severity score. The URL for the CVE-2021-3690 entry is CVE-2021-3690, offering a comprehensive overview of the vulnerability details.

CVSS 3 Score Breakdown: Severity Assessment

The CVSS (Common Vulnerability Scoring System) v3 score for CVE-2021-3690 is 7.5, indicating a high-severity vulnerability. This score is derived from a combination of base score metrics that assess the exploitability and impact of the vulnerability. Understanding the components of the CVSS score provides valuable insights into the severity and potential risks associated with the vulnerability.

Exploitability Metrics

The exploitability metrics evaluate how easily the vulnerability can be exploited by an attacker. The following metrics contribute to the exploitability score:

  • Attack Vector: Network (N) - This indicates that the vulnerability can be exploited over a network, meaning an attacker can initiate an attack remotely without requiring local access to the system. This broadens the attack surface and increases the potential for exploitation.
  • Attack Complexity: Low (L) - This signifies that the vulnerability is relatively easy to exploit. It does not require specialized skills, resources, or conditions, making it more accessible to a wider range of attackers.
  • Privileges Required: None (N) - This means that the attacker does not need any privileges or authentication to exploit the vulnerability. This further simplifies the exploitation process, as the attacker can trigger the vulnerability without any prior access or credentials.
  • User Interaction: None (N) - This indicates that no user interaction is required to exploit the vulnerability. The attacker can trigger the vulnerability without any actions from legitimate users, making it more stealthy and easier to execute.
  • Scope: Unchanged (U) - The scope being unchanged indicates that the vulnerability's impact is limited to the affected component (Undertow) and does not extend to other parts of the system. While the impact is contained, the high availability impact still results in a high severity.

Impact Metrics

The impact metrics assess the potential consequences of a successful exploit. The following metrics contribute to the impact score:

  • Confidentiality Impact: None (N) - This indicates that the vulnerability does not lead to any compromise of confidential information. The attacker cannot gain unauthorized access to sensitive data through this vulnerability.
  • Integrity Impact: None (N) - This means that the vulnerability does not allow the attacker to modify or corrupt data. The integrity of the system and its data remains unaffected by this vulnerability.
  • Availability Impact: High (H) - This signifies that the vulnerability has a significant impact on the availability of the system. As explained earlier, the vulnerability leads to memory exhaustion, which can cause the server to crash or become unresponsive, resulting in a denial-of-service.

CVSS 3 Score Calculator

For more detailed information on CVSS3 scores and their calculation, you can refer to the CVSS 3.0 calculator available at https://www.first.org/cvss/calculator/3.0. This tool allows you to input the various metrics and calculate the overall CVSS score, providing a deeper understanding of the severity assessment.

Suggested Fix and Mitigation Strategies

The suggested fix for CVE-2021-3690 is to upgrade the undertow-core library to a version that addresses the vulnerability. The recommended versions are io.undertow:undertow-websockets-jsr:2.0.40.Final and 2.2.10.Final. These versions contain the necessary patches to mitigate the buffer leak issue and prevent potential denial-of-service attacks.

Upgrade Version: The Primary Solution

The most effective way to address this vulnerability is to upgrade the affected library to a patched version. Upgrading ensures that the latest security fixes are applied, reducing the risk of exploitation. The fix resolution, as indicated in the vulnerability details, suggests upgrading to io.undertow:undertow-websockets-jsr:2.0.40.Final or 2.2.10.Final. This upgrade will resolve the memory leak issue in WebSocket PONG message handling, thereby preventing the denial-of-service vulnerability.

Origin and Release Date

The fix for this vulnerability originates from https://issues.redhat.com/browse/UNDERTOW-1935, which provides detailed information about the issue and its resolution. The release date for the fix is August 23, 2022, coinciding with the public disclosure of the vulnerability. Timely application of this fix is essential to protect systems from potential attacks.

Detailed Steps for Mitigation

To effectively mitigate the CVE-2021-3690 vulnerability, follow these steps:

  1. Identify Affected Systems: Determine all systems and applications that use the vulnerable undertow-core-2.2.16.Final.jar library. This includes reviewing dependency trees and software bills of materials (SBOMs).
  2. Plan the Upgrade: Develop a plan for upgrading the library, considering potential impacts on application functionality and compatibility. Schedule a maintenance window if necessary.
  3. Backup: Before initiating the upgrade, create a backup of the affected systems and applications. This ensures that you can revert to a stable state if any issues arise during the upgrade process.
  4. Upgrade the Library: Replace the vulnerable undertow-core-2.2.16.Final.jar with the recommended patched version (2.0.40.Final or 2.2.10.Final). Use your build tool (e.g., Maven, Gradle) to update the dependency.
  5. Test: After the upgrade, thoroughly test the application to ensure that the fix has been applied correctly and that no new issues have been introduced. This includes functional testing, performance testing, and security testing.
  6. Monitor: Continuously monitor the system for any signs of exploitation or unexpected behavior. Implement logging and alerting mechanisms to detect potential attacks.

Conclusion: Securing Your Applications Against CVE-2021-3690

The CVE-2021-3690 vulnerability poses a significant risk to applications using the undertow-core-2.2.16.Final.jar library. By understanding the technical details of the vulnerability, its potential impact, and the steps required for mitigation, developers and security professionals can effectively protect their systems. Upgrading to the patched versions (2.0.40.Final or 2.2.10.Final) is the primary solution, and following the detailed mitigation steps ensures a comprehensive approach to securing your applications against this high-severity vulnerability. Prioritizing security measures and staying informed about potential vulnerabilities are crucial for maintaining a robust and secure software environment.