CVE-2026-102861: Microsoft SharePoint Server Privilege Escalation

CVE-2026-102861 Overview

CVE-2026-102861 is a missing authorization vulnerability in Microsoft Office SharePoint that allows an authenticated attacker to elevate privileges across a network. The flaw maps to CWE-862: Missing Authorization and affects Microsoft SharePoint Server subscription edition. Microsoft published the advisory through the Microsoft Security Update Guide.

An attacker with low-privilege credentials can invoke SharePoint functionality without the required authorization checks. Successful exploitation yields high impact to confidentiality, integrity, and availability of the targeted SharePoint deployment.

Critical Impact
Authenticated attackers can elevate privileges across SharePoint Server subscription edition, enabling unauthorized access to site content, administrative functions, and sensitive enterprise data.

Affected Products

Microsoft SharePoint Server (subscription edition)
SharePoint sites and services relying on the vulnerable authorization logic
Downstream integrations consuming SharePoint APIs on affected servers

Discovery Timeline

2026-10-13 - CVE-2026-102861 published to the National Vulnerability Database
2026-10-14 - Last updated in NVD database

Technical Details for CVE-2026-102861

Vulnerability Analysis

The vulnerability stems from missing authorization enforcement in Microsoft SharePoint Server. A code path accessible to authenticated users fails to validate whether the caller holds the required permissions before executing a privileged operation. This condition is classified under CWE-862: Missing Authorization.

An authorized attacker with low privileges on the SharePoint instance can issue network requests that trigger the unprotected function. The server processes the request as if the caller were entitled to it, granting access to resources or actions that should be restricted to administrators or higher-privileged roles. Because the attack originates over the network and requires no user interaction, exploitation can be fully scripted against reachable SharePoint endpoints.

The EPSS probability stands at 0.698%, indicating current prediction data does not forecast widespread exploitation in the near term. However, SharePoint remains a high-value target in enterprise environments, and missing authorization issues historically attract adversary attention once technical details become public.

Root Cause

The root cause is an incomplete authorization check on a server-side handler within SharePoint. The handler trusts authenticated session context without verifying that the caller’s role or permission set authorizes the requested action. This design flaw allows horizontal and vertical privilege escalation depending on the exposed function.

Attack Vector

Exploitation requires network access to the SharePoint server and valid low-privilege credentials. The attacker sends crafted HTTP requests to the vulnerable endpoint and reaches privileged functionality without additional authorization prompts. No user interaction is required, and the attack complexity is low.

No public proof-of-concept exploit is currently listed, and the vulnerability is not present on the CISA Known Exploited Vulnerabilities list at the time of publication. Refer to the Microsoft Security Update Guide for authoritative technical details.

Detection Methods for CVE-2026-102861

Indicators of Compromise

Unexpected administrative actions performed by low-privilege SharePoint accounts, such as permission changes, site collection modifications, or feature activations.
HTTP requests to SharePoint endpoints by accounts whose role should not grant access to those handlers.
Creation of new site collection administrators, farm-level users, or elevated groups outside of normal change windows.

Detection Strategies

Correlate SharePoint Unified Logging Service (ULS) entries with Windows Security event logs to identify authenticated users invoking privileged operations outside their role scope.
Baseline normal API call patterns per user role and alert on deviations, especially requests to administrative handlers from standard contributor or reader accounts.
Review IIS logs on SharePoint front-end servers for unusual POST requests targeting administrative endpoints from unexpected client IP ranges.

Monitoring Recommendations

Forward SharePoint ULS, IIS, and Windows event logs to a centralized analytics platform for continuous correlation and historical hunting.
Enable auditing on SharePoint site collections for permission changes, user additions, and administrative actions.
Monitor Active Directory and Entra ID for sudden group membership changes that may indicate successful privilege escalation.

How to Mitigate CVE-2026-102861

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update Guide to all affected SharePoint Server subscription edition instances.
Inventory SharePoint farms and prioritize patching for internet-exposed or multi-tenant deployments.
Audit SharePoint user and group permissions and revoke standing access that is no longer required.

Patch Information

Microsoft has released a security update addressing the missing authorization check. Administrators should install the patch on all SharePoint Server subscription edition servers, including front-end and application tier nodes. Validate the update by confirming the installed build version matches the fixed release documented in the Microsoft advisory.

Workarounds

Restrict network access to SharePoint administrative endpoints using firewall rules, reverse proxy policies, or Web Application Firewall (WAF) controls.
Enforce multi-factor authentication on all SharePoint user accounts to raise the cost of credential-based access required for exploitation.
Reduce the number of accounts with authenticated access to sensitive SharePoint sites until patching is complete.

bash

# Verify installed SharePoint Server build on affected hosts
Get-SPFarm | Select-Object BuildVersion
Get-WmiObject -Class Win32_Product | Where-Object { $_.Name -like "*SharePoint*" } | Select-Object Name, Version