⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● High · CVSS 8.8

How to Fix CVE-2026-40370: Arbitrary File Read in Microsoft SQL Server 2016 Service Pack 3 (GDR)

Other vulnerabilities in the same area that are worth patching alongside this one:

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 8.8 - High
Actively exploited?Not currently listed in CISA KEV
Affected13.0.0 < 13.0.6490.1, 13.0.0 < 13.0.7085.1, 14.0.0 < 14.0.3530.2, 14.0.0 < 14.0.2110.2, 15.0.0.0 < 15.0.4470.1, 15.0.0 < 15.0.2170.1, and others
Fixed inSee vendor advisory
Type (CWE)CWE-73: External Control of File Name or Path

What is CVE-2026-40370?

CVE-2026-40370 is an arbitrary file read flaw in Microsoft SQL Server 2016 Service Pack 3 (GDR). An authenticated or unauthenticated request can read files outside the intended path scope, exposing configuration, secrets, or other sensitive content. Vendor description: External control of file name or path in SQL Server allows an authorized attacker to execute code over a network.

Why this CVE matters

Arbitrary file read against a management product almost always exposes credentials, session secrets, or configuration. Treat any disclosure of this kind as a credential-rotation event in addition to a patching event.

For deployments of Microsoft SQL Server 2016 Service Pack 3 (GDR) that have been exposed to the public internet during the disclosure window, the operating assumption should be that scanning has already happened. Even where exploitation has not been publicly observed, scanning for the vulnerable fingerprint is cheap and routine. Patching closes the door; log review and credential rotation close out the rest of the response.

Am I affected?

You are affected if your installation matches any of these version ranges:

Check your installed version against the list above. If you cannot determine the version, treat the system as affected and follow the upgrade path below.

On Windows, check the product's installed version via Settings - Apps - Installed apps, or run Get-Package from PowerShell to enumerate installed versions.

How to fix CVE-2026-40370

  1. Read the vendor advisory in full: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40370
  2. Upgrade Microsoft SQL Server 2016 Service Pack 3 (GDR) to the patched build listed in the vendor advisory.
  3. Back up the configuration (and database, where applicable) before upgrading.
  4. Apply the patch in a maintenance window. For HA pairs, upgrade the standby node first, fail over, then upgrade the former primary.
  5. Restart the affected service so the patched binary loads, then verify the new version (see verification section).

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Apply the Microsoft security update for Microsoft SQL server 2016 service pack 3 (gdr)

Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40370


# Confirm the patch is missing on this host.
Get-Hotfix -ErrorAction SilentlyContinue | Sort-Object InstalledOn -Descending |
  Select-Object -First 10

# Install the latest cumulative + security rollup that ships the fix for Microsoft SQL Server 2016 Service Pack 3 (GDR).
Install-Module PSWindowsUpdate -Force -SkipPublisherCheck
Import-Module PSWindowsUpdate
Get-WindowsUpdate -AcceptAll -Install -AutoReboot

# After reboot, verify the patched build is in place (13.0.6490.1).
Get-ComputerInfo -Property WindowsVersion, OsBuildNumber, OsHardwareAbstractionLayer


# Inventory missing patches across many Windows hosts via Ansible (winrm).
ansible windows -m win_updates -a "category_names=SecurityUpdates state=installed"

Verify the fix landed


# Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40370
# 1. Confirm the running version matches the fixed-in version listed above.

# 2. Re-scan with your vulnerability scanner (Nessus, Qualys, Tenable, OpenVAS).
#    The scanner should no longer flag this CVE on the patched target.

# 3. Inspect recent service / kernel logs for crash-loops or rollback events.
journalctl -u <service> --since "10 minutes ago"
dmesg --since "10 minutes ago"

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If you cannot patch immediately

No official workaround exists beyond restricting network exposure to the affected component. Apply the vendor patch as the primary remediation.

How to verify the fix worked

If your installation was internet-reachable during the disclosure window, treat log review as part of the remediation rather than an optional follow-up. Look for unusually long URI paths containing traversal sequences, unexpectedly large responses from the affected endpoint, and outbound requests from the application to internal addresses or cloud-metadata endpoints. Treat any sensitive file the bug could disclose as exposed.

Frequently asked questions

Is CVE-2026-40370 being exploited in the wild?

Public exploitation has not been confirmed by CISA at the time of writing. Treat the patch as time-sensitive anyway; reports often lag actual abuse.

Will a WAF or IDS rule fully mitigate CVE-2026-40370?

No. Network-layer filters can reduce noise and slow opportunistic scanners, but they will not stop a determined attacker. The vendor patch is the only durable fix.

How long should I plan for the upgrade?

Typical vendor-documented upgrade windows for Microsoft SQL Server 2016 Service Pack 3 (GDR) run from a few minutes to under an hour depending on cluster size. Test in a staging environment first and follow the vendor's documented HA upgrade order.

References

*This guide was assembled from the official vendor advisory, the NVD record, and the CISA KEV catalog entry on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*