CVE-2026-26115: SQL Server 2016 Privilege Escalation Bug

CVE-2026-26115 Overview

CVE-2026-26115 is an elevation of privilege vulnerability in Microsoft SQL Server caused by improper validation of a specified input type [CWE-1287]. An authenticated attacker can send crafted input over the network to elevate privileges on the database server. The flaw affects SQL Server 2016, 2017, 2019, 2022, and 2025 across x64 platforms. Microsoft tracks the issue through its Security Update Guide, and the CVE was published to the National Vulnerability Database (NVD) on March 10, 2026.

Critical Impact
Authenticated network attackers can elevate privileges on affected SQL Server instances, compromising the confidentiality, integrity, and availability of hosted databases.

Affected Products

Microsoft SQL Server 2016 (x64)
Microsoft SQL Server 2017 (x64)
Microsoft SQL Server 2019 (x64)
Microsoft SQL Server 2022 (x64)
Microsoft SQL Server 2025 (x64)

Discovery Timeline

2026-03-10 - CVE-2026-26115 published to NVD
2026-03-13 - Last updated in NVD database

Technical Details for CVE-2026-26115

Vulnerability Analysis

The vulnerability stems from improper validation of object types within SQL Server. When the database engine processes specific input, it fails to confirm that the supplied value matches the expected type before acting on it. An authenticated user can submit crafted data that the server processes in a privileged context. The result is an elevation of privilege from a low-privilege database account to a higher-privilege role on the server.

The issue is classified as Improper Validation of Specified Type of Input [CWE-1287]. Microsoft's advisory confirms exploitation requires network access and valid credentials but no user interaction. Successful exploitation produces a full compromise of the database service, including read, write, and availability impact on the affected instance.

Root Cause

The root cause is the absence of a strict type check on at least one user-controlled input path inside SQL Server. The engine accepts a value of an unexpected type and uses it in an operation that should be restricted by role or scope. This breaks the trust boundary between low-privilege database principals and privileged server contexts.

Attack Vector

An attacker authenticates to the SQL Server instance with any valid login, including a low-privilege account. The attacker then issues a crafted query, stored procedure call, or other database operation that supplies an input of an unexpected type. Because the operation runs in a higher trust context, the server executes attacker-controlled logic with elevated privileges. The attack works across the network and does not require local access or user interaction.

No public proof-of-concept code is available for CVE-2026-26115 at the time of writing. Refer to the Microsoft Security Update Guide for vendor-supplied technical details.

Detection Methods for CVE-2026-26115

Indicators of Compromise

Unexpected role membership changes or new sysadmin, db_owner, or server-role assignments tied to low-privilege logins.
Stored procedure or query executions that pass parameters of unusual types, especially against system catalog or extended stored procedures.
Authentication events from low-privilege accounts followed by privileged DDL or xp_cmdshell activity.
Outbound network connections initiated by sqlservr.exe to unexpected destinations after suspicious query activity.

Detection Strategies

Enable SQL Server Audit at the server level to log SERVER_ROLE_MEMBER_CHANGE_GROUP, SERVER_PERMISSION_CHANGE_GROUP, and failed permission checks.
Baseline normal query patterns per login and alert on deviations involving type-cast errors or repeated conversion failures preceding privileged actions.
Correlate Windows Security event logs from the SQL Server host with database audit events to identify privilege transitions.
Hunt for anomalous child processes of sqlservr.exe, which often indicates post-exploitation activity following privilege escalation.

Monitoring Recommendations

Forward SQL Server audit logs and Windows event logs to a centralized SIEM for correlation with identity and endpoint telemetry.
Monitor for sudden growth in high-privilege session counts on database servers exposed to application tiers.
Track logins originating from application service accounts performing administrative actions outside expected workflows.

How to Mitigate CVE-2026-26115

Immediate Actions Required

Apply the Microsoft security update for CVE-2026-26115 to all SQL Server 2016, 2017, 2019, 2022, and 2025 instances.
Inventory all SQL Server hosts and confirm patch deployment status against the Microsoft Security Update Guide.
Restrict network access to SQL Server TCP port 1433 and dynamic ports using host and network firewalls.
Rotate credentials for any database login suspected of misuse following review of audit logs.

Patch Information

Microsoft has issued security updates for all affected versions. Administrators should consult the Microsoft Security Update Guide for CVE-2026-26115 for the correct cumulative update or GDR package matching each SQL Server build. Apply updates in a staged manner, validating application compatibility before broad rollout.

Workarounds

Enforce least privilege by removing unnecessary server-role memberships and database-level permissions from application logins.
Disable unused features such as xp_cmdshell, CLR integration, and linked servers where not required by the workload.
Require strong authentication and limit SQL Server logins to trusted network segments using IPsec or private endpoints.
Place SQL Server instances behind a database firewall or proxy that inspects and constrains query patterns until patching is complete.

bash

# Configuration example: restrict SQL Server exposure and validate patch level
# 1. Confirm SQL Server build after patching
sqlcmd -S <server> -Q "SELECT SERVERPROPERTY('ProductVersion'), SERVERPROPERTY('ProductLevel');"

# 2. Disable xp_cmdshell if not required
sqlcmd -S <server> -Q "EXEC sp_configure 'show advanced options', 1; RECONFIGURE; \
EXEC sp_configure 'xp_cmdshell', 0; RECONFIGURE;"

# 3. Restrict inbound access to SQL Server port on Windows host
netsh advfirewall firewall add rule name="SQL-Restrict-1433" dir=in action=block protocol=TCP localport=1433 remoteip=any
netsh advfirewall firewall add rule name="SQL-Allow-AppTier" dir=in action=allow protocol=TCP localport=1433 remoteip=<app-tier-subnet>