CVE-2024-38023: Microsoft SharePoint Server RCE Vulnerability

CVE-2024-38023 Overview

CVE-2024-38023 is a Remote Code Execution (RCE) vulnerability affecting Microsoft SharePoint Server. This vulnerability stems from insecure deserialization (CWE-502), which allows authenticated attackers with Site Owner permissions or higher to execute arbitrary code on the SharePoint server. The flaw enables malicious actors to compromise SharePoint environments through network-based attacks without requiring user interaction.

Critical Impact

Authenticated attackers with elevated privileges can achieve remote code execution on vulnerable SharePoint servers, potentially leading to complete system compromise, data exfiltration, and lateral movement within enterprise networks.

Affected Products

• Microsoft SharePoint Server Subscription Edition
• Microsoft SharePoint Server 2019
• Microsoft SharePoint Server 2016 Enterprise Edition

Discovery Timeline

• July 9, 2024 - CVE-2024-38023 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-38023

Vulnerability Analysis

This vulnerability exploits an insecure deserialization flaw in Microsoft SharePoint Server. Deserialization vulnerabilities occur when an application reconstructs objects from serialized data without proper validation, allowing attackers to inject malicious serialized payloads that execute arbitrary code upon processing.

In the context of SharePoint, the vulnerability allows authenticated users with Site Owner permissions or higher to craft malicious payloads that, when processed by the SharePoint server, result in arbitrary code execution with the privileges of the SharePoint application pool identity. This typically provides extensive access to the underlying server and connected resources.

The vulnerability requires network access and high privileges (Site Owner or above), but once these prerequisites are met, exploitation does not require any user interaction, making it particularly dangerous in environments where Site Owner permissions have been broadly distributed.

Root Cause

The root cause is improper handling of serialized data within SharePoint Server components. The application fails to adequately validate or sanitize incoming serialized objects before deserializing them, creating an opportunity for attackers to inject malicious payloads. This class of vulnerability (CWE-502 - Deserialization of Untrusted Data) has been a recurring security concern in enterprise applications that process complex object serialization.

Attack Vector

The attack is executed over the network by an authenticated attacker who possesses Site Owner privileges or higher on the target SharePoint site. The attacker crafts a malicious serialized payload containing code execution primitives and submits it to a vulnerable SharePoint endpoint. When the server processes the request and deserializes the malicious object, the attacker's code executes in the context of the SharePoint server.

The attack flow typically involves:

1. Authenticating to SharePoint with Site Owner or equivalent privileges
2. Identifying a vulnerable deserialization endpoint
3. Crafting a malicious serialized payload using known .NET deserialization gadget chains
4. Submitting the payload to the vulnerable endpoint
5. Achieving code execution when the server deserializes the malicious object

For detailed technical information regarding exploitation mechanics, refer to the Microsoft Security Update Guide.

Detection Methods for CVE-2024-38023

Indicators of Compromise

• Unusual process spawning from SharePoint application pool processes (w3wp.exe)
• Unexpected outbound network connections from SharePoint servers
• Anomalous file creation or modification in SharePoint directories
• PowerShell or command shell execution originating from IIS worker processes

Detection Strategies

• Monitor SharePoint ULS logs for deserialization errors or unusual object processing failures
• Implement web application firewall rules to detect and block known .NET deserialization payloads
• Deploy endpoint detection and response (EDR) solutions to identify suspicious process chains originating from SharePoint services
• Review Windows Security Event logs for suspicious process creation events (Event ID 4688) linked to SharePoint processes

Monitoring Recommendations

• Enable enhanced auditing on SharePoint servers to capture detailed request information
• Establish baseline behavior for SharePoint application pools and alert on deviations
• Monitor for known deserialization gadget chain signatures in network traffic
• Implement file integrity monitoring on critical SharePoint server directories

How to Mitigate CVE-2024-38023

Immediate Actions Required

• Apply the Microsoft security update for CVE-2024-38023 immediately on all affected SharePoint servers
• Review and restrict Site Owner permissions to only essential personnel
• Audit current Site Owner assignments across all SharePoint sites and remove unnecessary elevated privileges
• Implement network segmentation to limit access to SharePoint servers from untrusted network segments

Patch Information

Microsoft has released security patches addressing this vulnerability as part of their July 2024 security updates. Administrators should apply the appropriate cumulative update for their SharePoint Server version. Detailed patch information and download links are available in the Microsoft Security Update Guide.

Ensure all SharePoint Server instances are updated:

• SharePoint Server Subscription Edition: Apply the latest cumulative update
• SharePoint Server 2019: Apply the July 2024 security update
• SharePoint Server 2016: Apply the July 2024 security update

Workarounds

• Restrict Site Owner permissions to the minimum number of trusted users until patching is complete
• Implement strict network access controls limiting which clients can reach SharePoint servers
• Enable Windows Defender Application Control (WDAC) to restrict unauthorized code execution
• Consider temporarily disabling non-essential SharePoint features that may expose deserialization endpoints

# PowerShell: Audit current Site Owner assignments across SharePoint sites
# Run on SharePoint Management Shell to identify users with elevated permissions
Get-SPSite -Limit All | ForEach-Object {
    $site = $_
    $web = $site.RootWeb
    $owners = $web.SiteGroups | Where-Object { $_.Name -like "*Owner*" }
    foreach ($group in $owners) {
        Write-Output "Site: $($site.Url) - Group: $($group.Name) - Members: $($group.Users | Select-Object -ExpandProperty LoginName)"
    }
}