CVE-2026-69804: Microsoft SharePoint Server Race Condition

CVE-2026-69804 Overview

CVE-2026-69804 is a Time-of-Check Time-of-Use (TOCTOU) race condition [CWE-367] in Microsoft SharePoint Server that permits an authorized attacker to execute code over a network. An attacker with valid low-privileged credentials can win a race window between a security check and a subsequent resource use, causing SharePoint to operate on attacker-controlled state. Successful exploitation yields high impact to confidentiality, integrity, and availability of the SharePoint environment.

Critical Impact
Authenticated network attackers can achieve remote code execution on SharePoint Server by exploiting a race between validation and use, potentially compromising site content, backend databases, and service account credentials.

Affected Products

Microsoft SharePoint Server (Subscription Edition)
Deployments exposing SharePoint web front-ends to authenticated users
On-premises SharePoint farms with default access configurations

Discovery Timeline

2026-09-08 - CVE-2026-69804 published to NVD
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-69804

Vulnerability Analysis

The flaw is a TOCTOU race condition inside Microsoft SharePoint Server. SharePoint validates a property, permission, or resource state at one point in a request handler, then acts on that same resource later without re-validating. An authenticated attacker who can concurrently modify the checked resource between those two operations forces the server to use the modified state during the privileged operation.

The race window enables the server to execute code paths intended for validated inputs against attacker-substituted content. Because the attack results in code execution within the SharePoint worker process, the attacker gains the privileges of the SharePoint application pool identity. This typically exposes SharePoint content databases, secure store credentials, and adjacent farm services.

The attack complexity is high because the attacker must reliably win the race window, which depends on server load, request timing, and thread scheduling. Exploitation requires low privileges but no user interaction. The current EPSS probability is 0.509%.

Root Cause

The root cause is non-atomic handling of a security-sensitive resource in SharePoint request processing. A property or authorization check and its dependent operation are separated in time without a lock, immutable snapshot, or re-check pattern. Concurrent requests from the same authorized principal can alter the underlying object between the check and use, invalidating the trust decision that SharePoint made.

Attack Vector

Exploitation occurs over the network against a SharePoint web endpoint. The attacker authenticates with any valid low-privilege account, then issues parallel requests: one triggering the vulnerable code path, and one modifying the resource being validated. When the modification lands inside the race window, SharePoint uses the swapped resource and executes attacker-controlled code. No user interaction is required. Public proof-of-concept code is not currently available, and the vulnerability is not listed in the CISA KEV catalog.

Detection Methods for CVE-2026-69804

Indicators of Compromise

Bursts of near-simultaneous requests from a single authenticated user targeting the same SharePoint object identifier or list item.
Unexpected w3wp.exe child processes such as cmd.exe, powershell.exe, or rundll32.exe under the SharePoint application pool identity.
New or modified files under SharePoint hive directories (%CommonProgramFiles%\Microsoft Shared\Web Server Extensions\16\) outside of patch windows.
Anomalous outbound network connections from SharePoint web front-end servers to attacker infrastructure.

Detection Strategies

Enable SharePoint Unified Logging Service (ULS) verbose logging and correlate repeated permission checks against the same object identifier within millisecond windows.
Deploy endpoint telemetry on SharePoint servers to flag process lineage where w3wp.exe spawns interpreters or LOLBins.
Alert on IIS access logs showing high-frequency parallel POST requests from the same authenticated session to the same resource endpoint.

Monitoring Recommendations

Baseline normal request concurrency per authenticated user and alert on statistically significant deviations against SharePoint web front-ends.
Monitor SharePoint application pool identities for lateral movement patterns including SMB access to file shares and SQL queries outside content database scope.
Forward IIS, ULS, and Windows Security logs to a centralized analytics platform for cross-source correlation.

How to Mitigate CVE-2026-69804

Immediate Actions Required

Apply the security update referenced in the Microsoft Security Update Guide for CVE-2026-69804 to all SharePoint Server Subscription Edition farms.
Inventory all SharePoint accounts and disable or rotate credentials for accounts that do not require active access.
Restrict SharePoint web front-end exposure so only authenticated users on trusted networks can reach the application.
Review audit logs for anomalous authenticated activity in the weeks preceding patch deployment.

Patch Information

Microsoft has published fix guidance in the Microsoft Security Response Center advisory. Administrators should apply the referenced cumulative update to every SharePoint Server in the farm, then run PSConfig to complete the upgrade sequence. Verify the farm build number matches the patched version reported by Microsoft after deployment.

Workarounds

Enforce least privilege on SharePoint sites and remove authenticated user access from sensitive site collections until patches are deployed.
Place SharePoint front-ends behind a reverse proxy or Web Application Firewall configured to rate-limit concurrent requests per session against the same URI.
Run SharePoint application pools under low-privilege service accounts and prohibit interactive logon or SQL sysadmin membership.

bash

# Example IIS rate limiting via Dynamic IP Restrictions module
appcmd.exe set config /section:system.webServer/security/dynamicIpSecurity /denyByConcurrentRequests.enabled:true /denyByConcurrentRequests.maxConcurrentRequests:10