CVE-2026-67376: SQL Server Integer Overflow DOS Vulnerability

CVE-2026-67376 Overview

CVE-2026-67376 is an integer overflow vulnerability in Microsoft SQL Server that allows an unauthenticated remote attacker to trigger a denial-of-service condition over the network. The flaw is classified under [CWE-190] Integer Overflow or Wraparound. An attacker can send crafted network traffic to a vulnerable SQL Server instance and cause the service to become unavailable, disrupting database-dependent applications. Microsoft published the advisory on September 8, 2026, and no authentication or user interaction is required to exploit the issue.

Critical Impact
Unauthenticated attackers can remotely crash or hang Microsoft SQL Server instances, disrupting availability for every application dependent on the affected database.

Affected Products

Microsoft SQL Server (specific supported versions listed in the Microsoft CVE-2026-67376 Update Guide)

Discovery Timeline

2026-09-08 - CVE CVE-2026-67376 published to NVD
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-67376

Vulnerability Analysis

CVE-2026-67376 stems from an integer overflow or wraparound condition in code paths reachable over the network in Microsoft SQL Server. When a specially crafted request supplies values that exceed the expected numeric bounds, the affected arithmetic operation wraps around. This produces an undersized allocation, an out-of-bounds access, or an invalid loop count that terminates the SQL Server process. The result is loss of database availability without any impact on confidentiality or integrity.

Availability disruption in a core database service typically cascades to every dependent application, ETL job, and reporting workload. Recovery requires the SQL Server service to restart, during which pending transactions may fail and clients may time out.

Root Cause

The root cause is improper validation of numeric input during request parsing or processing, categorized as [CWE-190] Integer Overflow or Wraparound. Arithmetic performed on attacker-controlled length or count fields exceeds the maximum value of the underlying integer type, producing an unintended small or negative result. That value then flows into memory operations that assume a valid, bounded quantity.

Attack Vector

Exploitation is remote and network-based, with no privileges or user interaction required. An attacker who can reach the SQL Server listener (default TCP port 1433) sends a malformed protocol message that triggers the overflow. Because SQL Server is often exposed inside application tiers with broad reachability, lateral movement from a compromised host can be sufficient. No verified public proof-of-concept code is available at the time of publication; refer to the Microsoft CVE-2026-67376 Update Guide for authoritative technical details.

Detection Methods for CVE-2026-67376

Indicators of Compromise

Unexpected termination or repeated restarts of the sqlservr.exe process on database hosts.
SQL Server error log entries showing access violations, stack dumps, or minidumps generated near the time of anomalous traffic.
Bursts of malformed Tabular Data Stream (TDS) traffic on TCP 1433 or configured SQL Server ports from unexpected source addresses.

Detection Strategies

Monitor Windows Event Log for Service Control Manager events indicating MSSQLSERVER service crashes or unexpected stops.
Alert on high rates of failed client connections or TCP resets targeting SQL Server listeners.
Correlate SQL Server dump file creation in the LOG directory with inbound network events from untrusted sources.

Monitoring Recommendations

Baseline normal TDS traffic patterns and flag unusual packet sizes or malformed protocol handshakes.
Track SQL Server availability with synthetic transactions to detect brief outages that may indicate exploitation attempts.
Forward SQL Server error logs and Windows Application logs to a centralized analytics platform for anomaly detection.

How to Mitigate CVE-2026-67376

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft CVE-2026-67376 Update Guide to all affected SQL Server instances.
Inventory every SQL Server deployment, including containerized and cloud-hosted instances, to ensure complete patch coverage.
Restrict inbound access to SQL Server ports so only trusted application servers can reach the listener.

Patch Information

Microsoft has released an update addressing CVE-2026-67376. Consult the Microsoft CVE-2026-67376 Update Guide for the specific cumulative update or GDR package corresponding to each supported SQL Server version and build.

Workarounds

Place SQL Server behind a firewall or network security group that permits access only from authorized application subnets.
Disable direct internet exposure of TCP 1433 and any custom SQL Server listener ports.
Require connections through a jump host or database proxy that can enforce protocol validation until patching is complete.

bash

# Example: restrict SQL Server access with Windows Firewall to a trusted subnet
New-NetFirewallRule -DisplayName "SQL Server 1433 - Trusted App Tier" `
  -Direction Inbound `
  -Protocol TCP `
  -LocalPort 1433 `
  -RemoteAddress 10.20.30.0/24 `
  -Action Allow

New-NetFirewallRule -DisplayName "Block SQL Server 1433 - Default Deny" `
  -Direction Inbound `
  -Protocol TCP `
  -LocalPort 1433 `
  -Action Block