CVE-2026-67389 Overview
CVE-2026-67389 is an out-of-bounds read vulnerability in Microsoft SQL Server that allows an authorized attacker to disclose information over a network. The flaw is tracked under CWE-125 and stems from improper bounds checking during processing of certain server-side operations. Successful exploitation exposes memory contents to a low-privileged database user, potentially leaking sensitive data resident in the SQL Server process address space.
Critical Impact
An authenticated attacker with low privileges can read out-of-bounds memory from a SQL Server instance and exfiltrate confidential data over the network without user interaction.
Affected Products
- Microsoft SQL Server (see the Microsoft Security Advisory for the authoritative list of affected versions and builds)
Discovery Timeline
- 2026-09-08 - CVE CVE-2026-67389 published to NVD
- 2026-09-08 - Last updated in NVD database
Technical Details for CVE-2026-67389
Vulnerability Analysis
The vulnerability is an out-of-bounds read in Microsoft SQL Server. When SQL Server processes a specific class of input, it reads beyond the intended buffer boundary and returns memory contents that were never meant to be exposed. The exposed memory can include cached query data, authentication material, or other tenant information that the querying principal is not authorized to see.
Exploitation requires network access to the SQL Server endpoint and valid low-privileged credentials. No user interaction is required, and the attack complexity is low. Confidentiality is directly impacted; integrity and availability remain unaffected because the primitive is limited to memory disclosure.
The EPSS probability is 0.714% with a percentile of 51.6, indicating that active exploitation is not currently expected but remains plausible once technical details or a proof of concept surface publicly.
Root Cause
The root cause is a missing or insufficient bounds check on a read operation within SQL Server, characteristic of CWE-125. A length or index value is trusted or computed incorrectly, allowing the server to dereference memory outside the intended structure. Microsoft has not published a technical root-cause writeup; refer to the Microsoft Security Advisory for vendor guidance.
Attack Vector
An attacker authenticates to a SQL Server instance with any valid low-privileged account and issues crafted queries or requests that trigger the vulnerable code path. The server returns memory content beyond the intended buffer as part of the response. The attacker parses the response client-side to reconstruct disclosed memory. Because the vector is network-based, exposed SQL Server endpoints and multi-tenant database environments carry the highest risk.
No public proof-of-concept code is available at this time. Refer to the Microsoft Security Advisory for further technical details.
Detection Methods for CVE-2026-67389
Indicators of Compromise
- Repeated queries from a single low-privileged principal producing anomalously large or malformed result sets.
- Unexpected T-SQL errors related to buffer or datatype handling immediately preceding successful queries from the same session.
- Outbound data transfers from database accounts that historically issue only routine read queries.
Detection Strategies
- Enable SQL Server Audit for SCHEMA_OBJECT_ACCESS_GROUP and FAILED_DATABASE_AUTHENTICATION_GROUP to correlate low-privileged access patterns with unusual query volumes.
- Baseline query fingerprints per principal and alert on new or malformed query shapes issued by non-administrative accounts.
- Inspect Extended Events sessions for repeated execution of built-in functions returning oversized binary or string data.
Monitoring Recommendations
- Forward SQL Server audit logs and Windows security events to a centralized analytics platform for correlation.
- Monitor egress volumes from database service accounts and alert on deviations from established baselines.
- Track authentication activity for dormant or service accounts that suddenly begin issuing ad-hoc queries.
How to Mitigate CVE-2026-67389
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft Security Advisory to all affected SQL Server instances.
- Inventory SQL Server principals and revoke unnecessary logins, focusing on shared or legacy low-privileged accounts.
- Restrict TCP 1433 and any custom SQL Server listener ports to trusted application subnets only.
Patch Information
Microsoft has published guidance and updates through the Microsoft Security Response Center. Consult the Microsoft Security Advisory for the specific cumulative update or GDR package that applies to your SQL Server version and edition. Apply the update in a staged fashion using standard change-management procedures.
Workarounds
- Enforce network-level isolation so that SQL Server endpoints are not directly reachable from user or internet-facing networks.
- Apply the principle of least privilege by removing unnecessary db_datareader, VIEW SERVER STATE, and VIEW ANY DEFINITION grants.
- Require strong authentication and enable multi-factor authentication on jump hosts used to reach SQL Server management interfaces.
# Example: restrict SQL Server access to a specific application subnet on Windows
New-NetFirewallRule -DisplayName "Restrict SQL 1433 to AppTier" `
-Direction Inbound -Protocol TCP -LocalPort 1433 `
-RemoteAddress 10.20.30.0/24 -Action Allow
New-NetFirewallRule -DisplayName "Block SQL 1433 from all other sources" `
-Direction Inbound -Protocol TCP -LocalPort 1433 `
-Action Block
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
