CVE-2026-67641: SQL Server Integer Overflow DOS Vulnerability

CVE-2026-67641 Overview

CVE-2026-67641 is an integer overflow vulnerability [CWE-190] in Microsoft SQL Server. An authorized attacker can trigger the flaw over a network to cause a denial-of-service (DoS) condition against the database engine. The issue affects availability but does not compromise confidentiality or integrity of stored data.

Exploitation requires low-privilege authenticated access to the SQL Server instance and no user interaction. Successful exploitation can render the database unresponsive, disrupting applications and services that depend on it. Microsoft has published guidance in the Microsoft Security Response Center advisory.

Critical Impact
An authenticated network attacker can crash or hang SQL Server through arithmetic wraparound, resulting in service outages for dependent applications.

Affected Products

Microsoft SQL Server (see vendor advisory for affected build ranges)
Environments where low-privilege database logins are exposed to untrusted clients
Applications and services that rely on affected SQL Server instances for data access

Discovery Timeline

2026-09-08 - CVE-2026-67641 published to the National Vulnerability Database (NVD)
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-67641

Vulnerability Analysis

The flaw is an integer overflow or wraparound [CWE-190] within SQL Server request handling logic. When a specially crafted operation is processed, an arithmetic calculation exceeds the maximum value of its integer type and wraps to an unexpected value. That wrapped value is then used in subsequent processing, producing an inconsistent state that halts service.

The attack vector is Network, complexity is Low, and only low-level privileges are required. There is no impact on confidentiality or integrity; the outcome is loss of availability. Microsoft classifies the outcome as denial of service against the database engine.

Root Cause

The root cause is unchecked arithmetic on attacker-influenced input processed by SQL Server. Without proper bounds validation, a value crosses its numeric limit and wraps, leading to a corrupted size calculation or control value. The affected code path then operates on invalid state and terminates or hangs the service.

Attack Vector

An attacker with valid database credentials submits crafted input over the standard SQL Server network protocol. Because the vulnerability is reachable through normal client access, exposure is broadest in multi-tenant deployments and applications that grant users direct SQL access. No social engineering or user interaction is needed.

No public proof-of-concept exploit is currently listed for CVE-2026-67641. Refer to the Microsoft Vulnerability Update CVE-2026-67641 for authoritative technical detail and affected build information.

Detection Methods for CVE-2026-67641

Indicators of Compromise

Unexpected sqlservr.exe process crashes, restarts, or hangs correlated with authenticated client sessions
SQL Server error log entries indicating access violations, assertion failures, or stack dumps
Sudden spikes in failed queries or connection timeouts from application tiers depending on the database

Detection Strategies

Monitor SQL Server Extended Events and error logs for repeated engine faults tied to specific logins or source IPs
Correlate database availability alerts with authentication telemetry to identify the initiating principal
Baseline query patterns per login and flag anomalous request payloads targeting affected code paths

Monitoring Recommendations

Enable auditing for successful and failed logins to attribute DoS events to specific accounts
Forward SQL Server logs and Windows Application event logs to a centralized SIEM for correlation
Alert on repeated sqlservr.exe service restarts within short time windows on production instances

How to Mitigate CVE-2026-67641

Immediate Actions Required

Apply the security update referenced in the Microsoft Vulnerability Update CVE-2026-67641 advisory to all affected SQL Server instances
Inventory SQL Server deployments and prioritize internet-exposed or multi-tenant instances
Rotate or disable any low-privilege database logins that are no longer required

Patch Information

Microsoft has released a security update addressed through the Microsoft Security Response Center. Administrators should consult the Microsoft Vulnerability Update CVE-2026-67641 advisory for the specific cumulative update or GDR package aligned with each SQL Server version and branch.

Workarounds

Restrict network access to SQL Server TCP port 1433 and any custom listener ports using host and network firewalls
Enforce least privilege on database logins and remove unnecessary permissions from application accounts
Place SQL Server behind a private network segment and require VPN or bastion access for administrative connections

bash

# Configuration example: restrict SQL Server access to trusted subnets on Windows
New-NetFirewallRule -DisplayName "Restrict SQL Server 1433" `
  -Direction Inbound -Protocol TCP -LocalPort 1433 `
  -RemoteAddress 10.0.0.0/24 -Action Allow

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