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CVE-2024-21318: Remote Code Execution in Microsoft SharePoint Server via Deserialization

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Vulnerability Summary

Affected Products

Product Affected Versions
SharePoint Server Subscription Edition Before Jan 2024 updates
SharePoint Server 2019 Before Jan 2024 updates
SharePoint Server 2016 Enterprise Edition Before Jan 2024 updates

How the Exploit Works

CVE-2024-21318 is a remote code execution vulnerability in Microsoft SharePoint Server. The flaw stems from improper deserialization of untrusted data (CWE-502), which can occur when a Site Owner sends specially crafted input to a vulnerable API endpoint. If processed without sufficient validation, this input can trigger deserialization of malicious objects, leading to arbitrary code execution under the context of the SharePoint service process.

Conceptual Example Code

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A hypothetical exploit could look like this, illustrating how a malicious payload might be injected into a SharePoint request:

POST /_layouts/15/ProcessBatchData.aspx HTTP/1.1
Host: vulnerable-sharepoint.local
Content-Type: application/xml

<Batch>
<Method ID="1" Cmd="New">
<Field Name="ID">1</Field>
<Field Name="Title">Exploit</Field>
<Field Name="Payload"><![CDATA[<malicious_serialized_object>]]></Field>
</Method>
</Batch>

The Payload field here is assumed to contain a serialized object designed to execute code when deserialized improperly by the backend.

Potential Risks

Mitigation Recommendations

  • Apply Updates Immediately:

    • SharePoint Server SE: KB5002540

    • SharePoint Server 2019: KB5002539

    • SharePoint Server 2016: KB5002541

  • Restrict Site Owner Permissions: Only assign elevated SharePoint roles to trusted administrators.

  • Segment Your Network: Ensure SharePoint systems are isolated from external exposure and monitored for abnormal traffic.

  • Audit and Monitor Logs: Look for suspicious activity, especially new or unexpected batch requests.

Conclusion

CVE-2024-21318 poses a serious threat to organizations relying on Microsoft SharePoint for collaboration and document management. While the vulnerability requires authenticated access with Site Owner permissions, exploitation can lead to full system compromise. Administrators should apply patches released in January 2024 and implement security best practices to defend against this vector.

References

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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