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

Vulnerability Summary

• CVE ID: CVE-2024-21318

• Severity: High (CVSS Score: 8.8)

• Attack Vector: Network

• Privileges Required: Low (Site Owner permissions)

• User Interaction: None

• Impact: Remote Code Execution (RCE)

Affected Products

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

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

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

Potential Risks

• Execution of arbitrary code on the SharePoint Server

• Lateral movement within the internal network

• Access to sensitive corporate data

• Service disruption and possible data tampering

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

• Microsoft CVE-2024-21318 Advisory

• NVD Entry for CVE-2024-21318

• Rapid7 Report

• Tenable Analysis