Advisory · CVE-2026-70024
Stack overflow in Windows IIS allows unauthenticated code execution
Windows Internet Information Services (IIS) has a stack-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 Internet Information Services
- Identifier / CWE
- CVE-2026-70024
CWE-121 - Action timing
- Immediate
Explain it like I’m five
The web server's stack can be overrun by a crafted request, turning the front door of the site into the way in.
- 01Reach the component
An unauthenticated attacker sends crafted network traffic to a Windows system running Windows Internet Information Services.
- 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-2026-70024 in its October 2026 update guide: a stack-based buffer overflow (CWE-121) in Windows Internet Information Services 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 Internet Information Services 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 Internet Information Services while remediation is underway, especially for internet-facing instances.
- Review application and server logs for IIS worker process crashes, malformed requests in web logs, and new content or accounts on web servers.
- 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
An unauthenticated 9.8 in the web server itself is an internet-facing emergency. Patch IIS hosts first and check for planted content.