CVE-2023-29357

CVE-2023-29357: Microsoft SharePoint Server Elevation of Privilege

AI-generated analysis based on the vulnerability data on this page.

Summary

A critical elevation of privilege vulnerability in Microsoft SharePoint Server 2019 enables unauthenticated attackers on the network to bypass authentication/authorization controls and gain elevated privileges, resulting in high impact to confidentiality, integrity, and availability.

Background

Microsoft SharePoint Server is an on-premises enterprise collaboration and document management platform widely deployed in corporate environments. It provides web-based portals, document libraries, and team sites integrated with Active Directory. CVE-2023-29357 affects the SharePoint Server 2019 on-premises product line.

Root Cause

The vulnerability is classified under CWE-303: Incorrect Authentication or Authorization. The root cause lies in the SharePoint Server's authentication/authorization logic, which improperly validates or enforces access controls under certain conditions. This allows an attacker to escalate privileges without presenting valid credentials or by bypassing intended authorization checks. The exact code path is not publicly disclosed, but the weakness category points to a failure in the authentication/authorization pipeline.

Impact

• CVSS v3 Score: 9.8 (Critical)
• Attack Vector (AV): Network — exploitable remotely without local access.
• Attack Complexity (AC): Low — no special conditions or advanced techniques required.
• Privileges Required (PR): None — the attacker does not need valid credentials.
• User Interaction (UI): None — no victim action is needed.
• Scope (S): Unchanged — the vulnerable component is the only one impacted.
• Confidentiality (C): High — sensitive data can be accessed.
• Integrity (I): High — data and configuration can be modified.
• Availability (A): High — service disruption is possible.

This combination makes the vulnerability trivially exploitable over the network with full impact on the SharePoint Server and its underlying data.

Exploitation Walkthrough

Ethics caveat: This section provides generic, defensive awareness only. No weaponized exploit code or step-by-step attack instructions are included. The goal is to help defenders understand the attack surface.

An attacker positioned on the network (or with internet access if SharePoint is exposed) sends a crafted HTTP request to a SharePoint endpoint that triggers the authentication/authorization bypass. The request is designed to exploit the improper validation logic in the SharePoint authentication pipeline, allowing the attacker to act with elevated privileges. Because the attack requires no authentication and no user interaction, automated exploitation tools can scan for and target exposed SharePoint instances at scale.

Defenders should monitor for:

• Unusual HTTP requests to SharePoint API endpoints from unexpected source IPs.
• Requests to authentication-related endpoints that result in elevated access or administrative actions.
• Bursts of 401/403 responses followed by successful 200 responses from the same source, which may indicate a bypass attempt.

Affected and Patched Versions

• Affected: Microsoft SharePoint Server 2019 (confirmed via CPE data: cpe:2.3:a:microsoft:sharepoint_server:2019:*:*:*:*:*:*:*).
• Patched versions: Not specified in the available structured data. Refer to the Microsoft Security Response Center (MSRC) advisory for the specific security update and build numbers.

Remediation

1. Patch immediately: Apply the Microsoft security update referenced in the MSRC advisory for CVE-2023-29357. Given the EPSS and KEV status, this should be treated as an emergency patch.
2. Network segmentation: Restrict network access to SharePoint Server endpoints to authorized internal users and VPN-only segments. Do not expose SharePoint management interfaces to the internet.
3. Web Application Firewall (WAF): Deploy WAF rules to detect and block anomalous requests targeting SharePoint authentication endpoints.
4. Compensating controls: Enforce multi-factor authentication (MFA) for all administrative accounts where technically feasible. Review and harden SharePoint service account permissions.
5. Monitoring: Enable detailed logging on SharePoint IIS and application logs. Forward logs to a SIEM for correlation and alerting.

Detection

• SIEM / Log monitoring: Alert on successful administrative actions from non-administrative source IPs or service accounts.
• Network monitoring: Flag unexpected outbound connections from the SharePoint server or inbound connections from unusual geographic locations.
• Vulnerability scanning: Use authenticated and unauthenticated scans to verify the SharePoint build version and patch status.
• File integrity monitoring: Track changes to SharePoint configuration files and web.config that may indicate post-exploitation activity.

Assessment

• EPSS: 0.99649 with a 99.95th percentile ranking indicates near-certain exploitation probability in the wild. This is one of the highest EPSS scores observed and demands immediate action.
• KEV: The vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog, added on 2024-01-10, and is also flagged as EU-exploited (EUVD-2023-32930). Active exploitation is confirmed by multiple government agencies.
• Ransomware: The vulnerability has been associated with ransomware campaigns, elevating the business risk beyond data theft to operational paralysis.

Lessons:

1. Authentication/authorization flaws are high-value targets: Enterprise collaboration platforms like SharePoint hold sensitive documents and are often reachable from the network, making authentication bypasses especially dangerous.
2. EPSS + KEV should drive triage: When EPSS exceeds 0.99 and KEV is confirmed, patching should bypass normal change-control windows and be treated as an incident-response activity.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-29357
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-29357