CVE-2023-28288: SharePoint Foundation Spoofing Vulnerability

CVE-2023-28288 Overview

CVE-2023-28288 is a spoofing vulnerability affecting Microsoft SharePoint Server that allows authenticated attackers to perform Server-Side Request Forgery (SSRF) attacks. This vulnerability enables malicious actors with low-level privileges to manipulate server requests, potentially accessing internal resources, exfiltrating sensitive data, or pivoting to other systems within the network infrastructure.

Critical Impact

Authenticated attackers can leverage this SSRF vulnerability to access internal network resources, potentially exposing sensitive configuration data, internal services, and enabling lateral movement within the organization's infrastructure.

Affected Products

• Microsoft SharePoint Foundation 2013 SP1
• Microsoft SharePoint Server 2013 SP1 (Enterprise)
• Microsoft SharePoint Server 2016 (Enterprise)
• Microsoft SharePoint Server 2019
• Microsoft SharePoint Server Subscription Edition

Discovery Timeline

• April 11, 2023 - CVE-2023-28288 published to NVD
• January 1, 2025 - Last updated in NVD database

Technical Details for CVE-2023-28288

Vulnerability Analysis

This spoofing vulnerability is classified under CWE-918 (Server-Side Request Forgery), indicating that SharePoint Server improperly validates or sanitizes user-supplied URLs or request parameters. When exploited, the server can be tricked into making requests to arbitrary destinations on behalf of the attacker, bypassing network segmentation and firewall controls.

The attack requires authentication but only low-level privileges, making it accessible to any user with basic SharePoint access. Successful exploitation can lead to significant confidentiality and integrity impacts, as attackers can access internal resources and potentially modify server-side data or configurations.

Root Cause

The root cause of CVE-2023-28288 lies in insufficient validation of user-controlled input that is subsequently used to construct server-side HTTP requests. SharePoint Server fails to properly restrict the destination URLs or parameters, allowing authenticated users to manipulate the server into initiating requests to unintended internal or external endpoints. This architectural weakness in request handling enables SSRF attack patterns.

Attack Vector

The vulnerability is exploitable over the network by authenticated users. An attacker with valid SharePoint credentials can craft malicious requests that cause the SharePoint server to initiate connections to internal network resources, cloud metadata endpoints, or other sensitive services. The attack does not require user interaction, making it particularly dangerous in environments where SharePoint is accessible to many users.

The exploitation mechanism involves sending specially crafted requests to SharePoint Server that contain manipulated URL parameters or references. The server processes these requests without adequate validation, resulting in unintended outbound connections that can be used for reconnaissance, data exfiltration, or further attacks against internal infrastructure.

Detection Methods for CVE-2023-28288

Indicators of Compromise

• Unusual outbound HTTP/HTTPS requests from SharePoint servers to internal IP addresses or sensitive endpoints (e.g., 169.254.169.254 for cloud metadata)
• SharePoint application logs showing requests to internal resources that shouldn't be accessed by the web tier
• Network traffic anomalies where SharePoint servers connect to internal services or hosts they typically don't communicate with

Detection Strategies

• Monitor SharePoint ULS logs for suspicious URL patterns or requests containing internal IP addresses
• Implement network-level monitoring to detect SharePoint servers making unexpected outbound connections
• Deploy web application firewall (WAF) rules to detect and block SSRF attack patterns in incoming requests
• Enable detailed audit logging on SharePoint servers to track all authentication events and request patterns

Monitoring Recommendations

• Configure alerts for SharePoint servers attempting connections to internal metadata services or restricted network segments
• Implement egress filtering and monitor for policy violations from SharePoint server subnets
• Review SharePoint access logs regularly for authenticated users accessing unusual URL patterns or making high volumes of requests

How to Mitigate CVE-2023-28288

Immediate Actions Required

• Apply Microsoft's security update for CVE-2023-28288 immediately on all affected SharePoint deployments
• Review and restrict network access from SharePoint servers to internal resources using firewall rules
• Audit SharePoint user accounts and remove unnecessary access privileges
• Implement network segmentation to limit the blast radius of potential SSRF attacks

Patch Information

Microsoft has released security updates to address this vulnerability. Administrators should apply the appropriate patches for their SharePoint version as documented in the Microsoft Security Update Guide. The patches address the improper request validation that enables the SSRF attack vector.

For detailed technical information about the exploitation technique, security researchers can reference the Packet Storm Security Exploit Document.

Workarounds

• Implement strict egress filtering on SharePoint server networks to block unauthorized outbound connections
• Configure web application firewall rules to inspect and block requests containing internal IP addresses or suspicious URL patterns
• Limit authenticated user access to SharePoint to only those who require it
• Consider placing SharePoint servers in a dedicated network segment with controlled access to internal resources

# Example: Network firewall rule to restrict SharePoint server outbound access
# Block SharePoint servers from accessing internal metadata endpoints
# This is a conceptual example - adapt to your firewall platform

# Block access to cloud metadata services
iptables -A OUTPUT -s <sharepoint_server_ip> -d 169.254.169.254 -j DROP

# Block access to internal RFC1918 ranges (adjust based on legitimate needs)
iptables -A OUTPUT -s <sharepoint_server_ip> -d 10.0.0.0/8 -j LOG --log-prefix "SP_INTERNAL_ACCESS: "