CVE-2023-38177: Microsoft SharePoint Server RCE Flaw

CVE-2023-38177 Overview

CVE-2023-38177 is a remote code execution vulnerability affecting Microsoft SharePoint Server. This vulnerability allows an attacker with high privileges and adjacent network access to execute arbitrary code on vulnerable SharePoint Server installations. The vulnerability is classified as an insecure deserialization flaw (CWE-502), which can be exploited to achieve code execution within the context of the SharePoint server process.

Critical Impact

Successful exploitation of this vulnerability enables attackers to execute arbitrary code on Microsoft SharePoint servers, potentially leading to complete system compromise, data exfiltration, and lateral movement within enterprise networks.

Affected Products

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

Discovery Timeline

• November 14, 2023 - CVE-2023-38177 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-38177

Vulnerability Analysis

This vulnerability exists due to improper handling of serialized data within Microsoft SharePoint Server. The flaw relates to insecure deserialization (CWE-502), a class of vulnerabilities where untrusted data is deserialized without proper validation, allowing attackers to manipulate the deserialization process to achieve malicious outcomes.

The attack requires the adversary to have high privileges on the SharePoint server and be positioned on an adjacent network. While these prerequisites limit the attack surface, the potential impact is significant as successful exploitation grants full confidentiality, integrity, and availability compromise of the affected system.

Root Cause

The root cause of CVE-2023-38177 is insecure deserialization within Microsoft SharePoint Server components. When the application deserializes untrusted data without adequate security controls, an attacker can craft malicious serialized objects that, when processed, execute arbitrary code. This type of vulnerability is particularly dangerous in enterprise collaboration platforms like SharePoint, where the server often has access to sensitive organizational data and network resources.

Attack Vector

The attack vector for this vulnerability is adjacent network-based, meaning the attacker must have network adjacency to the target SharePoint server. Additionally, the attacker requires high-level privileges on the system to exploit this vulnerability. The attack does not require user interaction and can be executed with low complexity once the attacker has established the necessary positioning and privileges.

An attacker would need to craft a specially crafted serialized payload and deliver it to a vulnerable SharePoint Server component that processes the malicious data. Upon deserialization, the payload would execute arbitrary code with the privileges of the SharePoint server process.

Detection Methods for CVE-2023-38177

Indicators of Compromise

• Unusual or unauthorized deserialization activity in SharePoint server logs
• Unexpected process spawning from SharePoint application pools (e.g., w3wp.exe spawning command interpreters)
• Anomalous network connections originating from SharePoint servers to internal or external addresses
• Unauthorized file creation or modification in SharePoint installation directories

Detection Strategies

• Monitor SharePoint ULS (Unified Logging Service) logs for serialization-related errors or exceptions
• Implement network segmentation monitoring to detect adjacent network reconnaissance or lateral movement attempts
• Deploy endpoint detection and response (EDR) solutions to identify suspicious process behavior on SharePoint servers
• Configure application-level logging to capture deserialization events and flag unusual patterns

Monitoring Recommendations

• Enable verbose logging on SharePoint servers to capture detailed request and response data
• Implement real-time alerting for high-privilege account activity on SharePoint infrastructure
• Monitor Windows Security Event logs for privilege escalation attempts (Event IDs 4672, 4673)
• Conduct regular security assessments of SharePoint server configurations and patch levels

How to Mitigate CVE-2023-38177

Immediate Actions Required

• Apply the Microsoft security update for CVE-2023-38177 immediately on all affected SharePoint installations
• Review and restrict high-privilege account access to SharePoint servers
• Implement network segmentation to limit adjacent network access to SharePoint infrastructure
• Audit current SharePoint server configurations for any signs of compromise

Patch Information

Microsoft has released a security update to address this vulnerability. Organizations should apply the patch available through the Microsoft Security Update Guide for CVE-2023-38177. The update addresses the insecure deserialization flaw in the affected SharePoint Server versions including SharePoint Enterprise Server 2016, SharePoint Server 2019, and SharePoint Server Subscription Edition.

Workarounds

• Restrict network access to SharePoint servers using firewall rules and network access control lists (ACLs)
• Implement strict privilege management policies, limiting the number of high-privilege accounts with access to SharePoint
• Deploy web application firewalls (WAF) with rules to detect and block suspicious serialized payloads
• Consider temporarily isolating vulnerable SharePoint servers until patches can be applied

# Example: Restrict network access to SharePoint using Windows Firewall
# Block adjacent network access except from trusted management subnets
netsh advfirewall firewall add rule name="Block Adjacent Network to SharePoint" dir=in action=block remoteip=192.168.0.0/16
netsh advfirewall firewall add rule name="Allow Trusted Management Subnet" dir=in action=allow remoteip=10.0.1.0/24