CVE-2026-67393 Overview
CVE-2026-67393 is a buffer over-read vulnerability [CWE-126] in Microsoft SQL Server that allows an authorized attacker to disclose information over a network. The flaw enables an authenticated adversary to read memory beyond the intended buffer boundary, exposing sensitive data resident in the SQL Server process. Microsoft published the advisory through the Security Update Guide. Exploitation requires low privileges and no user interaction, but the impact is limited to confidentiality.
Critical Impact
An authenticated attacker with network access to a vulnerable SQL Server instance can read adjacent memory contents, potentially exposing credentials, query data, or other sensitive information held in server memory.
Affected Products
- Microsoft SQL Server (refer to the Microsoft Security Update Guide for the definitive list of affected versions and builds)
Discovery Timeline
- 2026-09-08 - CVE-2026-67393 published to NVD
- 2026-09-08 - Last updated in NVD database
Technical Details for CVE-2026-67393
Vulnerability Analysis
The vulnerability is a buffer over-read categorized as [CWE-126]. SQL Server reads past the end of an intended buffer while processing attacker-influenced input, returning unintended memory contents to the requester. The condition affects confidentiality only; integrity and availability are not impacted according to the CVSS vector. Exploitation requires an authenticated session with the database engine, which limits reach to users who already possess valid SQL Server credentials or an application-level pivot.
Information disclosure through over-read primitives is often used by adversaries to defeat memory protections, harvest secrets, or stage follow-on attacks against the database and connected systems. Because the disclosure occurs over the network protocol used by SQL Server, exposed instances reachable from application tiers or lateral positions are the primary risk surface.
Root Cause
The root cause is improper validation of a length or index value used during a buffer read operation inside SQL Server. When the computed read extends beyond the allocated buffer, adjacent memory is returned to the caller. Microsoft has not published low-level technical details for the affected component. Refer to the Microsoft Security Update Guide entry for CVE-2026-67393 for authoritative product and component details.
Attack Vector
An attacker authenticates to a target SQL Server instance over the network using valid credentials or an application account. The attacker then issues crafted requests that trigger the over-read code path. The server returns memory contents beyond the intended buffer boundary in its response. No user interaction is required, and the scope is unchanged.
No public proof-of-concept exploit is available at the time of publication, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The EPSS score is 0.736%.
Detection Methods for CVE-2026-67393
Indicators of Compromise
- Unusual query patterns from application service accounts, particularly repeated malformed or oversized parameter values targeting the same stored procedure or function.
- Unexpected authenticated sessions from hosts that do not normally interact with the SQL Server instance.
- Anomalous response sizes from SQL Server to specific queries that historically returned small result sets.
Detection Strategies
- Enable SQL Server Audit for FAILED_LOGIN_GROUP, SUCCESSFUL_LOGIN_GROUP, and database-level audit specifications to capture authentication and query activity.
- Baseline normal query patterns per application account and alert on statistical deviations in query structure, frequency, or response payload size.
- Correlate SQL Server error log entries with network telemetry to identify sessions issuing malformed protocol requests.
Monitoring Recommendations
- Forward SQL Server audit logs, error logs, and TDS-layer telemetry to a centralized analytics platform for retention and correlation.
- Monitor egress from database hosts for unexpected data volumes that could indicate exfiltration of disclosed memory contents.
- Review privileged database role assignments monthly and alert on additions to sysadmin, db_owner, or custom roles with broad query rights.
How to Mitigate CVE-2026-67393
Immediate Actions Required
- Apply the security update referenced in the Microsoft Security Update Guide for CVE-2026-67393 to all affected SQL Server instances.
- Inventory SQL Server deployments and prioritize patching for instances exposed to untrusted networks or shared-tenant applications.
- Rotate credentials for SQL Server logins that may have been exposed through memory disclosure on unpatched instances.
Patch Information
Microsoft has issued a security update for CVE-2026-67393. Consult the Microsoft Security Update Guide for the specific KB articles, cumulative updates, and build numbers that address the vulnerability across supported SQL Server versions.
Workarounds
- Restrict network access to SQL Server instances using firewall rules, network segmentation, and Azure Private Endpoints or VPC controls so that only trusted application tiers can reach the database.
- Enforce least-privilege on SQL logins and application service accounts; remove unnecessary permissions that would allow triggering vulnerable code paths.
- Require TLS for all SQL Server client connections and disable legacy authentication methods where feasible to limit unauthorized session establishment.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
