CVE-2024-38018: Microsoft SharePoint Server RCE Vulnerability

CVE-2024-38018 Overview

CVE-2024-38018 is a remote code execution vulnerability affecting Microsoft SharePoint Server. This vulnerability allows an authenticated attacker with Site Member permissions to execute arbitrary code on the SharePoint server remotely. The flaw stems from insecure deserialization (CWE-502) in the SharePoint Server application, which can be exploited over the network without user interaction.

Critical Impact

Successful exploitation allows authenticated attackers with low privileges to achieve full remote code execution on SharePoint servers, potentially compromising confidentiality, integrity, and availability of enterprise collaboration systems and sensitive data.

Affected Products

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

Discovery Timeline

• September 10, 2024 - CVE-2024-38018 published to NVD
• September 18, 2024 - Last updated in NVD database

Technical Details for CVE-2024-38018

Vulnerability Analysis

This remote code execution vulnerability in Microsoft SharePoint Server arises from insecure deserialization practices within the application. SharePoint Server fails to properly validate and sanitize serialized data before deserializing it, creating an opportunity for attackers to inject malicious payloads. When the vulnerable component processes specially crafted serialized objects, it can lead to arbitrary code execution within the context of the SharePoint application pool identity.

The vulnerability is particularly concerning because it requires only Site Member level permissions to exploit—a common privilege level in enterprise SharePoint environments. This low barrier to entry significantly expands the potential attacker pool to include any authenticated user with basic access to a SharePoint site.

Root Cause

The root cause of CVE-2024-38018 is insecure deserialization (CWE-502) within Microsoft SharePoint Server. The application deserializes untrusted data without sufficient validation, allowing attackers to craft malicious serialized objects that execute arbitrary code when processed by the server. This type of vulnerability occurs when applications deserialize data from untrusted sources without implementing proper type constraints, allowlists, or integrity checks on the serialized content.

Attack Vector

The attack is conducted over the network (Network attack vector) and requires low privileges—specifically, Site Member permissions on the target SharePoint site. No user interaction is required for exploitation, making this vulnerability particularly dangerous in environments where SharePoint sites have numerous authenticated users.

An attacker with Site Member access would craft a malicious serialized payload designed to exploit the deserialization flaw. When this payload is processed by the vulnerable SharePoint Server component, it triggers code execution with the privileges of the SharePoint application pool, potentially allowing the attacker to access sensitive data, modify content, install backdoors, or pivot to other systems on the network.

The vulnerability mechanism involves sending specially crafted requests containing malicious serialized objects to the SharePoint server. Technical details regarding the specific endpoint and payload structure should be obtained from the Microsoft Security Advisory.

Detection Methods for CVE-2024-38018

Indicators of Compromise

• Unusual serialized object payloads in SharePoint web requests, particularly those containing unexpected .NET type references
• Abnormal process spawning from SharePoint application pool worker processes (w3wp.exe)
• Suspicious network connections originating from SharePoint server processes to unexpected destinations
• Unexpected file system modifications or new files created in SharePoint directories

Detection Strategies

• Monitor SharePoint ULS logs for deserialization errors or exceptions indicating attempted exploitation
• Implement web application firewall rules to detect and block known deserialization attack patterns targeting SharePoint
• Deploy endpoint detection and response (EDR) solutions to identify malicious process behavior originating from IIS worker processes
• Review authentication logs for suspicious Site Member activity patterns preceding unusual server behavior

Monitoring Recommendations

• Enable enhanced logging for SharePoint Server to capture detailed request information
• Configure alerts for w3wp.exe processes executing unexpected child processes or making anomalous network connections
• Monitor for changes to SharePoint configuration files and web.config modifications
• Implement network segmentation monitoring to detect lateral movement attempts from SharePoint servers

How to Mitigate CVE-2024-38018

Immediate Actions Required

• Apply the security updates from Microsoft's September 2024 Patch Tuesday release immediately
• Review Site Member access lists and remove unnecessary user permissions pending patching
• Implement network segmentation to limit SharePoint server exposure
• Enable enhanced monitoring on SharePoint servers to detect exploitation attempts

Patch Information

Microsoft has released security updates to address this vulnerability as part of their September 2024 security updates. Administrators should apply the appropriate patch for their SharePoint Server version:

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

Detailed patch information and download links are available in the Microsoft Security Response Center advisory for CVE-2024-38018.

Workarounds

• Restrict Site Member permissions to only essential users until patches can be applied
• Implement additional network-level access controls to limit who can reach SharePoint servers
• Consider temporarily disabling non-essential SharePoint features that may expose deserialization endpoints
• Deploy web application firewall rules configured to detect and block serialization-based attacks

# Example: Review current Site Member permissions using SharePoint Management Shell
# Run this on your SharePoint server to audit site membership
Get-SPSite -Limit All | ForEach-Object {
    Get-SPWeb -Site $_ -Limit All | ForEach-Object {
        Write-Host "Site: $($_.Url)"
        $_.SiteGroups | Where-Object { $_.Name -like "*Member*" } | ForEach-Object {
            Write-Host "  Group: $($_.Name) - Users: $($_.Users.Count)"
        }
    }
}