CVE-2020-1439: SharePoint Enterprise Server RCE Vulnerability

CVE-2020-1439 Overview

A remote code execution vulnerability exists in PerformancePoint Services for Microsoft SharePoint Server when the software fails to properly validate the source markup of XML file input. This insecure deserialization vulnerability allows authenticated attackers to execute arbitrary code on the affected SharePoint server, potentially leading to complete system compromise.

Critical Impact

Authenticated attackers can achieve remote code execution on SharePoint servers through malicious XML payloads, potentially compromising confidentiality, integrity, and availability of enterprise collaboration infrastructure.

Affected Products

• Microsoft SharePoint Enterprise Server 2013 SP1
• Microsoft SharePoint Enterprise Server 2016
• Microsoft SharePoint Foundation 2013 SP1
• Microsoft SharePoint Server 2010 SP2
• Microsoft SharePoint Server 2019

Discovery Timeline

• 2020-07-14 - CVE-2020-1439 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-1439

Vulnerability Analysis

This vulnerability stems from insecure deserialization (CWE-502) in the PerformancePoint Services component of Microsoft SharePoint Server. The affected service processes XML file input without properly validating the source markup, creating an opportunity for attackers to inject malicious serialized objects. When the vulnerable component deserializes untrusted data, an attacker can manipulate the deserialization process to instantiate arbitrary objects and execute code within the context of the SharePoint application pool.

The vulnerability requires network access and low-privilege authentication to exploit, but once authentication is achieved, no user interaction is required for successful exploitation. The attack complexity is low, making this vulnerability particularly dangerous in enterprise environments where SharePoint serves as a central collaboration platform.

Root Cause

The root cause is inadequate input validation in the XML parsing functionality of PerformancePoint Services. The service accepts XML file input and processes it through a deserialization mechanism that fails to properly verify the integrity and safety of the serialized data. This allows attackers to craft malicious XML payloads containing serialized objects that execute code when deserialized by the vulnerable service.

Attack Vector

The attack is conducted over the network against the SharePoint server's PerformancePoint Services component. An attacker with valid SharePoint credentials can submit specially crafted XML files containing malicious serialized payloads. When the PerformancePoint service processes these files, the insecure deserialization triggers execution of the attacker's code with the privileges of the SharePoint application pool identity.

The exploitation flow involves:

1. Authenticating to the SharePoint environment with low-privilege credentials
2. Crafting a malicious XML payload with embedded serialized objects
3. Submitting the payload to the PerformancePoint Services endpoint
4. The service deserializes the payload without proper validation
5. Arbitrary code executes in the context of the SharePoint service account

Technical details about this vulnerability are available in the Zero Day Initiative Advisory ZDI-20-874.

Detection Methods for CVE-2020-1439

Indicators of Compromise

• Unusual XML file submissions to PerformancePoint Services endpoints
• Unexpected process spawning from SharePoint application pool worker processes (w3wp.exe)
• Anomalous network connections originating from SharePoint server processes
• Evidence of serialized object payloads in SharePoint logs or network traffic

Detection Strategies

• Monitor SharePoint ULS logs for errors related to XML parsing or deserialization failures in PerformancePoint Services
• Implement web application firewall rules to detect common deserialization attack patterns in XML payloads
• Enable Windows Event logging for process creation events to identify suspicious child processes of w3wp.exe
• Deploy endpoint detection and response (EDR) solutions to monitor SharePoint server behavior

Monitoring Recommendations

• Configure SharePoint diagnostic logging to capture detailed PerformancePoint Services activity
• Establish baseline behavior for SharePoint application pools and alert on deviations
• Monitor authentication logs for unusual access patterns to PerformancePoint features
• Implement network traffic analysis for SharePoint server communications

How to Mitigate CVE-2020-1439

Immediate Actions Required

• Apply Microsoft security updates immediately to all affected SharePoint Server installations
• Restrict access to PerformancePoint Services to only trusted users who require the functionality
• Review and audit SharePoint authentication logs for suspicious activity
• Consider temporarily disabling PerformancePoint Services if not business-critical until patching is complete

Patch Information

Microsoft has released security updates to address this vulnerability. Patches are available through Windows Update and the Microsoft Update Catalog. Organizations should apply the July 2020 security updates for their specific SharePoint version. Detailed patch information and deployment guidance is available in the Microsoft Security Advisory CVE-2020-1439.

Workarounds

• Limit network access to SharePoint servers using firewall rules and network segmentation
• Implement strict authentication requirements and multi-factor authentication for SharePoint access
• Disable PerformancePoint Services feature if not actively used in your organization
• Apply the principle of least privilege to SharePoint service accounts and user permissions

# PowerShell - Check if PerformancePoint Service Application is running
Get-SPServiceApplication | Where-Object {$_.TypeName -like "*PerformancePoint*"}

# If not required, disable the service application
$pps = Get-SPServiceApplicationPool -Identity "PerformancePoint Service Application"
Stop-SPServiceInstance -Identity $pps.Id