Advisory · CVE-2026-69634
Heap overflow in Windows iSCSI allows unauthenticated code execution
The Windows iSCSI component has a heap-based buffer overflow an unauthenticated attacker can trigger over the network to execute code. Microsoft rates it CVSS 3.1 9.8.
- Vendor
- Microsoft
- Product
- Windows iSCSI
- Identifier / CWE
- CVE-2026-69634
CWE-122 - Action timing
- Immediate
Explain it like I’m five
The component that connects Windows to network storage trusts incoming blocks too much, and an oversized one spills into code execution.
- 01Reach the component
An unauthenticated attacker sends crafted network traffic to a Windows system running Windows iSCSI.
- 02Memory flaw triggers
The component mishandles the input and corrupts or reuses memory outside its intended bounds.
- 03Code runs
The attacker gains code execution in the component's context on the target system.
What happened
Microsoft disclosed CVE-2026-69634 in its October 2026 update guide: a heap-based buffer overflow (CWE-122) in Windows iSCSI lets an unauthorized attacker execute code over a network.
Microsoft lists the affected Windows releases in its update guide. Apply the October 2026 security updates for your release rather than relying on a version guess here.
What to do
- Inventory every Windows iSCSI deployment, including test, training, and individually managed instances.
- Apply the vendor fix or upgrade exactly as directed in the linked vendor bulletin or advisory.
- Restrict network access to Windows iSCSI while remediation is underway, especially for internet-facing instances.
- Review application and server logs for iSCSI initiator crashes, storage disconnects outside maintenance, and unexpected traffic to storage ports.
- Check for accounts, content, or configuration created outside normal change processes, and rotate exposed credentials where access cannot be ruled out.
- Verify the deployed version or patch level after remediation.
Management note
iSCSI hosts are usually storage-adjacent and highly trusted. Patch quickly and check which networks can even reach the storage interfaces.