CVE-2017-20189

Comprehensive Technical Analysis of CVE-2017-20189

1. Vulnerability Assessment and Severity Evaluation

CVE ID: CVE-2017-20189 CVSS Score: 9.8

The vulnerability in Clojure before version 1.9.0 allows for the construction of a serialized object that can execute arbitrary code upon deserialization. This type of vulnerability is particularly severe because it can lead to remote code execution (RCE), which is one of the most critical types of security flaws. The high CVSS score of 9.8 underscores the critical nature of this vulnerability, indicating a high risk of exploitation with significant potential impact.

2. Potential Attack Vectors and Exploitation Methods

Attack Vectors:

• Untrusted Deserialization: The primary attack vector involves deserializing untrusted data. If an attacker can inject a malicious serialized object into a system that deserializes it, they can execute arbitrary code.
• Network Services: Any network service that accepts serialized objects from untrusted sources is at risk. This includes web applications, RPC services, and other network-facing components.

Exploitation Methods:

• Crafting Malicious Objects: An attacker can craft a serialized object that, when deserialized, executes malicious code. This can be done using tools like ysoserial, which is specifically designed to generate payloads for deserialization vulnerabilities.
• Injection Points: Identifying injection points where serialized data is accepted and processed is crucial. These points can be in web forms, API endpoints, or other data entry points.

3. Affected Systems and Software Versions

Affected Software:

• Clojure versions before 1.9.0

Systems at Risk:

• Any system running applications or services that use Clojure versions prior to 1.9.0 and deserialize untrusted data.
• Systems that rely on third-party libraries or frameworks that use vulnerable versions of Clojure.

4. Recommended Mitigation Strategies

Immediate Mitigation:

• Upgrade Clojure: Upgrade to Clojure version 1.9.0 or later, which includes the patch for this vulnerability.
• Disable Deserialization: If possible, disable deserialization of untrusted data.
• Input Validation: Implement strict input validation to ensure that only trusted data is deserialized.

Long-Term Mitigation:

• Code Review: Conduct a thorough code review to identify and mitigate any instances of unsafe deserialization.
• Security Training: Educate developers on the risks of deserialization and best practices for handling serialized data.
• Regular Updates: Ensure that all software dependencies are regularly updated to the latest versions to mitigate known vulnerabilities.

5. Impact on Cybersecurity Landscape

Deserialization vulnerabilities are a significant concern in the cybersecurity landscape due to their potential for remote code execution. This vulnerability highlights the importance of secure coding practices and the need for robust input validation and sanitization. The widespread use of Clojure in various applications underscores the potential impact of this vulnerability, making it a critical issue for organizations to address promptly.

6. Technical Details for Security Professionals

Vulnerability Details:

• The vulnerability arises from the ability to construct a serialized object that, upon deserialization, can execute arbitrary code. This is facilitated by the way Clojure handles classes during the deserialization process.
• The flaw is present in the deserialization mechanism of Clojure, which does not adequately validate or sanitize the serialized data, allowing for the execution of malicious code.

Exploit Examples:

• Tools like ysoserial can be used to generate payloads that exploit this vulnerability. The payloads can be crafted to execute commands, open reverse shells, or perform other malicious actions upon deserialization.

Patch Information:

• The vulnerability is addressed in Clojure version 1.9.0. The patch includes changes to the deserialization process to prevent the execution of arbitrary code.
• References to the patch and related advisories can be found in the provided URLs, including the commit in the Clojure GitHub repository and the vendor advisory on the Clojure Atlassian site.

References:

• Clojure Atlassian Advisory
• Clojure GitHub Commit
• ysoserial Pull Request
• HackMD Advisory
• Snyk Vulnerability Database

By understanding the technical details and implementing the recommended mitigation strategies, organizations can effectively protect their systems from this critical vulnerability.