CVE-2026-67386: SQL Server Information Disclosure Flaw

CVE-2026-67386 Overview

CVE-2026-67386 is an information disclosure vulnerability in Microsoft SQL Server caused by the use of an uninitialized resource [CWE-908]. An authorized attacker with low privileges can query the affected component over a network and receive residual data from memory that was never properly initialized. The flaw does not require user interaction and can leak sensitive server-side content to any authenticated database user.

The issue is tracked as a network-exploitable information disclosure affecting confidentiality only. Integrity and availability of the SQL Server instance are not directly impacted, but leaked memory may include credentials, query fragments, or other sensitive artifacts that enable follow-on attacks.

Critical Impact
An authenticated attacker can read uninitialized memory contents from a remote SQL Server instance, potentially exposing sensitive data resident in the process address space.

Affected Products

Microsoft SQL Server (versions listed in the Microsoft Security Update Guide advisory)

Discovery Timeline

2026-09-08 - CVE-2026-67386 published to NVD
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-67386

Vulnerability Analysis

The vulnerability is classified under [CWE-908]: Use of Uninitialized Resource. SQL Server allocates a memory buffer or resource but fails to fully initialize it before returning contents to a client. When the server serializes the response, residual bytes from prior allocations are transmitted along with legitimate data.

Exploitation requires authenticated access to the SQL Server instance. The attacker submits crafted queries or protocol requests that trigger the vulnerable code path. The server responds with data that includes uninitialized memory contents rather than zeroed or freshly populated bytes.

The leaked information may contain fragments of other users' query results, session tokens, connection metadata, or cached credential material. Repeated queries can be used to sample memory over time and reconstruct sensitive artifacts.

Root Cause

The root cause is a code path within SQL Server that allocates a buffer or structure without zeroing or fully populating it before serialization. When the response is sent to the client, stale bytes from prior heap or stack usage are included, resulting in an information leak.

Attack Vector

Exploitation occurs over the network using the Tabular Data Stream (TDS) protocol or another SQL Server client interface. The attacker must authenticate with a low-privilege database account. Once authenticated, they issue requests that exercise the vulnerable code path and parse the returned data for uninitialized memory contents.

Refer to the Microsoft Security Update Guide advisory for technical specifics on the affected component and query patterns.

Detection Methods for CVE-2026-67386

Indicators of Compromise

Repeated identical or near-identical queries from a single authenticated session that produce varying response sizes or content patterns.
Unusual volumes of small, targeted queries against system views or metadata endpoints from low-privilege accounts.
Client sessions issuing malformed or non-standard TDS requests that succeed without error.

Detection Strategies

Enable SQL Server Audit to record login events, query text, and session activity for all authenticated principals.
Baseline normal query volume and response size per user, then alert on statistical deviations from low-privilege accounts.
Correlate SQL Server audit logs with network flow data to identify sessions transferring anomalous data volumes.

Monitoring Recommendations

Forward SQL Server audit logs, Extended Events sessions, and Windows Security logs to a centralized analytics platform for correlation.
Monitor for privilege enumeration or reconnaissance activity that typically precedes exploitation of information disclosure flaws.
Track authentication patterns for service accounts and application logins to identify credential misuse against database endpoints.

How to Mitigate CVE-2026-67386

Immediate Actions Required

Apply the security update referenced in the Microsoft Security Update Guide advisory to all affected SQL Server instances.
Inventory all SQL Server deployments, including embedded and legacy instances, to confirm patch coverage.
Review database account privileges and revoke unnecessary login rights that could be leveraged for authenticated exploitation.

Patch Information

Microsoft has published a security update through the Microsoft Security Update Guide. Administrators should download and deploy the update corresponding to their SQL Server version and cumulative update level. Consult the vendor advisory for build numbers and installation guidance.

Workarounds

Restrict network access to SQL Server endpoints using firewall rules that limit connections to trusted application hosts.
Enforce least-privilege on all database accounts and remove interactive login rights from service accounts where feasible.
Require strong authentication and monitor for anomalous authenticated sessions until patching is complete.

bash

# Configuration example
# Restrict SQL Server TCP 1433 to trusted subnets on Windows
New-NetFirewallRule -DisplayName "SQL Server - Trusted Only" \
  -Direction Inbound -Protocol TCP -LocalPort 1433 \
  -RemoteAddress 10.0.10.0/24 -Action Allow

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