CVE-2023-36764: SharePoint Server Privilege Escalation

CVE-2023-36764 Overview

CVE-2023-36764 is an Elevation of Privilege vulnerability affecting Microsoft SharePoint Server. This vulnerability allows an authenticated attacker to escalate their privileges within the SharePoint environment, potentially gaining unauthorized access to sensitive resources and administrative functions. The vulnerability exists across multiple versions of SharePoint Server, including SharePoint Server 2016 Enterprise, SharePoint Server 2019, and SharePoint Server Subscription Edition.

Critical Impact

Authenticated attackers can exploit this vulnerability to elevate privileges, potentially gaining full control over SharePoint resources, accessing confidential data, and compromising organizational collaboration infrastructure.

Affected Products

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

Discovery Timeline

• 2023-09-12 - CVE-2023-36764 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-36764

Vulnerability Analysis

This Elevation of Privilege vulnerability in Microsoft SharePoint Server is associated with CWE-73 (External Control of File Name or Path). The vulnerability allows an authenticated user with low privileges to escalate their access rights within the SharePoint environment. Once exploited, the attacker can achieve high impact on confidentiality, integrity, and availability of the affected system.

The attack requires network access and can be executed with low attack complexity, meaning that an attacker with valid credentials and network connectivity to the SharePoint server can reliably exploit this vulnerability without requiring user interaction. The scope is unchanged, indicating that the compromised component does not affect resources beyond its security scope.

Root Cause

The root cause of CVE-2023-36764 is related to improper handling of external control of file names or paths (CWE-73). This weakness occurs when the application allows external input to influence or control file system paths without proper validation or sanitization. In the context of SharePoint Server, this can enable attackers to manipulate file paths in ways that bypass intended access controls, leading to privilege escalation.

Attack Vector

The attack vector for this vulnerability is network-based. An authenticated attacker with low-level privileges on the SharePoint server can craft malicious requests that exploit the path handling weakness. The exploitation does not require any user interaction, making it particularly dangerous in enterprise environments where SharePoint serves as a central collaboration platform.

The attack flow typically involves:

1. An attacker authenticates to the SharePoint server with a low-privileged account
2. The attacker crafts requests that manipulate file paths to access resources outside their intended scope
3. Through successful exploitation, the attacker gains elevated privileges within the SharePoint environment
4. The elevated access can be used to access sensitive documents, modify site configurations, or compromise other user accounts

Detection Methods for CVE-2023-36764

Indicators of Compromise

• Unusual access patterns from low-privileged SharePoint user accounts attempting to access administrative functions or restricted resources
• Unexpected file path traversal attempts or manipulation in SharePoint request logs
• Authentication events followed by rapid escalation to administrative operations
• Anomalous modifications to SharePoint site collections, permissions, or configurations by non-administrative accounts

Detection Strategies

• Monitor SharePoint ULS (Unified Logging Service) logs for suspicious file path manipulation patterns or unauthorized access attempts
• Implement audit logging for administrative actions and alert on activities performed by low-privileged accounts
• Deploy network monitoring to detect unusual API calls or requests to SharePoint endpoints
• Utilize SIEM solutions to correlate authentication events with subsequent privilege escalation indicators

Monitoring Recommendations

• Enable comprehensive SharePoint audit logging across all site collections and web applications
• Configure alerts for changes to site collection administrators, web application policies, and farm-level settings
• Implement user behavior analytics to detect deviation from normal access patterns for SharePoint users
• Regularly review SharePoint access logs and security audit reports for signs of privilege escalation attempts

How to Mitigate CVE-2023-36764

Immediate Actions Required

• Apply the Microsoft security update for CVE-2023-36764 immediately to all affected SharePoint Server installations
• Review SharePoint user accounts and remove unnecessary privileges following the principle of least privilege
• Audit recent SharePoint activity logs for any signs of exploitation prior to patching
• Ensure SharePoint servers are isolated from unnecessary network exposure and protected by appropriate firewalls

Patch Information

Microsoft has released security updates to address this vulnerability. The official security advisory and patch information can be found at the Microsoft Security Update Guide for CVE-2023-36764. Organizations should apply the appropriate security updates based on their SharePoint Server version:

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

Ensure that all cumulative updates and security patches are applied according to Microsoft's guidance.

Workarounds

• Implement strict network segmentation to limit access to SharePoint servers from untrusted network segments
• Enforce multi-factor authentication for all SharePoint users to add an additional layer of security
• Apply application-layer firewall rules to monitor and filter suspicious requests to SharePoint endpoints
• Conduct regular access reviews to ensure that user permissions align with job requirements and remove stale accounts

# Configuration example
# Verify SharePoint patch level using SharePoint Management Shell
Get-SPFarm | Select-Object BuildVersion

# Review site collection administrators
Get-SPSite -Limit All | ForEach-Object {
    Write-Host "Site: $($_.Url)"
    Get-SPUser -Web $_.Url -Limit All | Where-Object {$_.IsSiteAdmin -eq $true}
}

# Enable audit logging for SharePoint site collection
$site = Get-SPSite "https://sharepoint.contoso.com"
$site.Audit.AuditFlags = [Microsoft.SharePoint.SPAuditMaskType]::All
$site.Audit.Update()