CVE-2026-77485: SQL Server Use After Free Vulnerability

CVE-2026-77485 Overview

CVE-2026-77485 is a use-after-free vulnerability [CWE-416] in Microsoft SQL Server. An authorized local attacker can trigger the flaw to elevate privileges on the affected host. Microsoft published the advisory on September 8, 2026 through the MSRC Update Guide.

The vulnerability requires local access and valid low-privilege credentials on the SQL Server instance. Successful exploitation impacts confidentiality, integrity, and availability. Attack complexity is high, which reflects the timing and memory-state conditions required to reliably reuse freed memory during exploitation.

Critical Impact
An authorized local attacker who successfully exploits CVE-2026-77485 can elevate privileges on the SQL Server host, potentially reaching the security context of the database engine service account.

Affected Products

Microsoft SQL Server (versions listed in the Microsoft Update Guide)
Deployments where low-privileged database users can issue queries against the engine
Instances that have not applied the September 2026 Microsoft security update

Discovery Timeline

2026-09-08 - CVE-2026-77485 published to NVD
2026-09-09 - Last updated in NVD database

Technical Details for CVE-2026-77485

Vulnerability Analysis

CVE-2026-77485 is a use-after-free condition in Microsoft SQL Server. A use-after-free occurs when code references memory after it has been released back to the allocator. An attacker who can influence allocation and deallocation order may reuse the freed region with attacker-controlled data before the dangling pointer is dereferenced.

In SQL Server, this class of flaw typically arises in query processing, session state handling, or extended stored procedure code paths. When the freed object is reallocated with crafted contents, a subsequent dereference can redirect execution flow inside the sqlservr.exe process. Because the SQL Server service typically runs with elevated privileges relative to a low-privileged database login, successful exploitation yields local privilege escalation.

Root Cause

The root cause is improper lifetime management of a heap-allocated object [CWE-416]. Code paths continue to reference an object after the memory manager has freed it. Microsoft has not published low-level technical details describing the affected object or code path.

Attack Vector

The attack vector is local. An attacker must already hold valid credentials on the SQL Server instance and be able to submit queries or commands to the database engine. The attacker then triggers the vulnerable code path to reclaim the freed allocation with controlled data and force the process to dereference it. Attack complexity is high because the attacker must win a memory-state race to reliably control the reallocated content.

No public proof-of-concept exploit is available, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Refer to the Microsoft CVE-2026-77485 Update Guide for authoritative technical details.

Detection Methods for CVE-2026-77485

Indicators of Compromise

Unexpected crashes or access violations in sqlservr.exe, particularly with heap corruption signatures in Windows Error Reporting.
New or unexpected child processes spawned from the SQL Server service account.
Sudden privilege changes for database logins or the creation of new sysadmin-level accounts.
Anomalous execution of xp_cmdshell, CLR assemblies, or extended stored procedures from low-privileged accounts.

Detection Strategies

Enable and forward SQL Server audit logs, focusing on login activity, permission changes, and use of privileged stored procedures.
Monitor Windows event logs for sqlservr.exe crashes with exception codes indicating heap corruption such as 0xC0000374 or 0xC0000005.
Correlate query telemetry with process telemetry to identify low-privileged accounts triggering repeated engine faults.

Monitoring Recommendations

Baseline normal parent-child process relationships for the SQL Server service and alert on deviations.
Track application-tier authentication for reused or shared low-privilege database accounts that could be leveraged by an attacker.
Aggregate database, host, and identity telemetry into a central data lake to enable cross-source correlation of exploitation attempts.

How to Mitigate CVE-2026-77485

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-77485 Update Guide to all affected SQL Server instances.
Inventory SQL Server hosts and database logins to identify systems that expose query access to low-privileged users.
Rotate credentials for any database accounts suspected of misuse and review recent privilege grants.

Patch Information

Microsoft has released a security update addressing CVE-2026-77485. Consult the Microsoft CVE-2026-77485 Update Guide for the list of affected builds and the corresponding cumulative update or GDR package. Apply the update through Windows Update, WSUS, or your standard SQL Server patching process, and restart the database service to complete installation.

Workarounds

Restrict database login access to trusted principals and enforce least privilege on all SQL Server roles and permissions.
Disable unnecessary features such as xp_cmdshell, CLR integration, and legacy extended stored procedures where not required.
Isolate SQL Server hosts on segmented networks and prevent interactive logon by non-administrative users.
Run the SQL Server service under a dedicated low-privileged domain account to limit the blast radius of a successful escalation.

bash

# Configuration example: reduce attack surface on SQL Server
sqlcmd -S localhost -Q "EXEC sp_configure 'show advanced options', 1; RECONFIGURE;"
sqlcmd -S localhost -Q "EXEC sp_configure 'xp_cmdshell', 0; RECONFIGURE;"
sqlcmd -S localhost -Q "EXEC sp_configure 'clr enabled', 0; RECONFIGURE;"