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CVE-2021-21249 : Exploit Details and Defense Strategies

Discover the impact of CVE-2021-21249 on OneDev versions prior to 4.0.3, allowing post-auth remote code execution. Learn about the vulnerability and mitigation steps.

OneDev is an all-in-one devops platform with a vulnerability (CVE-2021-21249) that affects versions prior to 4.0.3. The issue involves YAML parsing, potentially leading to post-auth remote code execution through SnakeYaml. This critical vulnerability was addressed in version 4.0.3 by restricting class deserialization.

Understanding CVE-2021-21249

This section will cover the details of CVE-2021-21249, including its impact, technical details, and mitigation strategies.

What is CVE-2021-21249?

CVE-2021-21249 is a security vulnerability in OneDev versions before 4.0.3 that allows post-auth remote code execution due to unsafe YAML deserialization. Attackers can exploit this issue to instantiate arbitrary classes, leading to potential code execution.

The Impact of CVE-2021-21249

With a CVSS score of 9.6 (Critical), this vulnerability has a severe impact on confidentiality and integrity. An attacker can exploit it over a network with low privileges required, potentially altering system integrity and compromising sensitive data.

Technical Details of CVE-2021-21249

Let's delve into the technical aspects of CVE-2021-21249, exploring the vulnerability description, affected systems, and the exploitation mechanism.

Vulnerability Description

The vulnerability arises from insecure YAML parsing in OneDev, allowing the instantiation of arbitrary classes. This can be exploited by an attacker for post-auth remote code execution by loading user-controlled classes.

Affected Systems and Versions

OneDev versions prior to 4.0.3 are affected by this vulnerability. Users of these versions are at risk of exploitation and are advised to upgrade to the patched version.

Exploitation Mechanism

By leveraging SnakeYaml's YAML parsing, attackers can instantiate arbitrary classes like

javax.script.ScriptEngineManager
, enabling them to execute arbitrary code post-authentication.

Mitigation and Prevention

Protecting your system against CVE-2021-21249 is crucial. Here are some immediate steps and long-term security practices to consider:

Immediate Steps to Take

        Upgrade OneDev to version 4.0.3 or newer to prevent exploitation of this vulnerability.
        Monitor for any unusual system behavior that could indicate a successful attack.

Long-Term Security Practices

        Regularly update your software and keep track of security advisories to stay informed about potential threats.
        Implement network segmentation and least privilege access to limit the impact of security breaches.

Patching and Updates

Stay informed about security patches and updates released by OneDev. Apply them promptly to ensure that your system is protected against known vulnerabilities.

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