CVE-2026-67625: SQL Server Heap Buffer Overflow RCE Flaw

CVE-2026-67625 Overview

CVE-2026-67625 is a heap-based buffer overflow vulnerability in Microsoft SQL Server. An authenticated attacker can trigger the flaw over a network to execute arbitrary code in the context of the SQL Server process. The weakness is classified under [CWE-122], covering heap-based memory corruption.

Microsoft published the advisory on October 13, 2026. The vulnerability requires low privileges but high attack complexity, and successful exploitation changes scope with impact to confidentiality, integrity, and availability. No public proof-of-concept or in-the-wild exploitation has been reported at the time of publication.

Critical Impact

Authenticated network attackers can achieve code execution within the SQL Server process, potentially leading to full database compromise and lateral movement into connected systems.

Affected Products

• Microsoft SQL Server (specific build versions listed in the Microsoft advisory)

Discovery Timeline

• 2026-10-13 - CVE-2026-67625 published to NVD
• 2026-10-13 - Last updated in NVD database

Technical Details for CVE-2026-67625

Vulnerability Analysis

The vulnerability is a heap-based buffer overflow in SQL Server's handling of network-delivered input. When the server processes a specially crafted request, it writes beyond the bounds of a heap-allocated buffer. This corruption can be shaped to overwrite adjacent heap metadata or function pointers used later in execution.

Exploitation requires an authenticated session on SQL Server with at least low-privileged database access. The attack complexity is high because the attacker must manipulate heap layout and timing to achieve reliable code execution. Successful exploitation runs code in the SQL Server service account, which commonly holds broad access to databases, backups, and linked servers.

The scope change recorded in the advisory indicates that impact can extend beyond the vulnerable component, affecting the underlying host or integrated services. The EPSS score at publication reflects a low near-term exploitation probability, but the impact profile makes this a priority patch for internet-adjacent or multi-tenant SQL Server deployments.

Root Cause

The root cause is improper validation of input size before copying data into a fixed-size heap buffer. SQL Server's parser or protocol handler accepts attacker-controlled length values without enforcing an upper bound, allowing the write operation to exceed the allocated region. This corresponds to the [CWE-122] weakness pattern.

Attack Vector

The attack vector is network-based and requires valid authentication to the SQL Server instance. An attacker with low-privileged database credentials sends a crafted request through the Tabular Data Stream (TDS) protocol or an exposed SQL interface. The request contains data engineered to overflow a heap buffer during server-side parsing, enabling code execution if heap grooming succeeds.

See the Microsoft Security Update CVE-2026-67625 advisory for protocol-level technical details.

Detection Methods for CVE-2026-67625

Indicators of Compromise

• Unexpected crashes or access violation events in the sqlservr.exe process logged in the Windows Application event log
• SQL Server error log entries referencing stack dumps, memory violations, or minidump creation around authenticated session activity
• Anomalous child processes spawned by the SQL Server service account, such as cmd.exe, powershell.exe, or rundll32.exe
• Outbound network connections initiated by sqlservr.exe to untrusted or external hosts

Detection Strategies

• Monitor authentication logs for low-privileged SQL logins issuing unusual query patterns or protocol-level anomalies
• Correlate SQL Server crash dumps with preceding authenticated session traffic to identify exploitation attempts
• Hunt for process lineage anomalies where sqlservr.exe is the parent of interactive shells or scripting hosts

Monitoring Recommendations

• Enable SQL Server audit for successful and failed logins and high-privilege statement execution
• Forward Windows Security, Application, and SQL Server logs to a centralized SIEM for correlation
• Baseline normal SQL Server process behavior to detect deviations in memory usage, child processes, and network egress

How to Mitigate CVE-2026-67625

Immediate Actions Required

• Apply the Microsoft security update referenced in the Microsoft Security Update CVE-2026-67625 advisory to all affected SQL Server instances
• Inventory SQL Server deployments, including development, test, and embedded instances, and prioritize internet-exposed systems
• Rotate credentials for any low-privileged SQL accounts that may have been exposed or shared across environments
• Review database-level permissions and remove unnecessary logins to shrink the authenticated attack surface

Patch Information

Microsoft released a security update addressing CVE-2026-67625 on October 13, 2026. Patch details, affected build numbers, and download links are available in the Microsoft Security Update CVE-2026-67625 advisory. Apply the update through Windows Update, WSUS, or the Microsoft Update Catalog depending on your patch management workflow.

Workarounds

• Restrict network access to SQL Server TCP port 1433 and dynamic ports using host and network firewalls, limiting connectivity to known application servers
• Enforce least-privilege database roles so that compromised low-privileged credentials provide minimal exploitation leverage
• Require TLS for SQL Server connections and enable Force Encryption to reduce exposure of authentication traffic
• Disable unused SQL Server features and endpoints, including external linked servers and remote query capabilities, where not required

# Example: Restrict SQL Server inbound access with Windows Firewall
New-NetFirewallRule -DisplayName "SQL Server - Restricted" `
  -Direction Inbound `
  -Protocol TCP `
  -LocalPort 1433 `
  -RemoteAddress 10.0.0.0/24 `
  -Action Allow

# Block all other inbound 1433 traffic
New-NetFirewallRule -DisplayName "SQL Server - Block Other" `
  -Direction Inbound `
  -Protocol TCP `
  -LocalPort 1433 `
  -Action Block