Microsoft IIS Buffer Overflow Lets Attackers Run Code Remotely

An attacker who targets Windows Internet Information Services can now execute arbitrary code on the affected system without needing prior access. This capability arises from a stack-based buffer overflow flaw within the web server software. Microsoft has published an official advisory regarding this vulnerability, which carries the identifier CVE-2026-70024.

The issue allows an unauthorized user to run commands remotely over a network connection. Security teams must treat this as a high-priority risk because the attacker does not need to authenticate before attempting exploitation. The potential for remote code execution means that a successful attack could lead to full system compromise, allowing the adversary to install malware, steal data or move laterally within the network environment.

In plain English

Windows Internet Information Services is a web server program that helps organizations host websites and applications on Windows computers. A buffer overflow happens when a program tries to store more data in a memory space than it can handle. In this specific case, the overflow occurs on the stack, which is a part of memory used for temporary data processing.

When the server processes certain requests, it may not check the size of the incoming data properly. This oversight allows an attacker to send specially crafted information that overwrites adjacent memory. By controlling what gets overwritten, the attacker can trick the server into running their own malicious code instead of the intended program instructions.

The background

Microsoft released the details of this vulnerability through its Security Update Guide. The advisory describes the issue as a remote code execution flaw that affects Windows Internet Information Services. The National Vulnerability Database also lists CVE-2026-70024 with a severity rating of 9.8, which is classified as critical.

The NVD record identifies two specific weakness types associated with this flaw: CWE-20, which relates to improper input validation, and CWE-121, which covers stack-based buffer overflows. These classifications help security researchers understand the technical nature of the defect. The combination of these weaknesses creates a scenario where external attackers can exploit the server from a distance without needing local access or valid credentials.

What changes now

Organizations running Windows Internet Information Services need to assess their exposure to this remote code execution risk. Since the vulnerability allows network-based attacks, any instance of the software accessible from the internet is potentially at risk. Security operations teams should monitor their web servers for unusual activity that might indicate an exploitation attempt.

While the source material does not confirm the immediate availability of a patch, the critical rating suggests that remediation will be urgent once updates are released. Until then, restricting access to the web servers and implementing strict network segmentation can help reduce the attack surface. Teams should also review their incident response plans to ensure they are prepared to handle potential compromises resulting from this type of buffer overflow.

What made it possible

Buffer overflow vulnerabilities typically arise when software fails to validate the size of incoming data before storing it in memory. This weakness allows attackers to overwrite critical memory structures, such as return addresses on the stack, to redirect program execution. In intrusion scenarios, this technique serves as an initial access vector, enabling remote code execution without authentication.

Security teams usually mitigate this risk by enforcing strict input validation and using memory-safe programming practices. Organizations should check whether their web servers expose unnecessary endpoints to untrusted networks. Implementing network-level controls, such as firewalls and intrusion prevention systems, can help block malicious payloads before they reach the vulnerable application.

Background: Firewalls

Start with a strict deny-all baseline. Define only the traffic you explicitly need. Apply rules in small batches during maintenance windows. Verify connectivity after each change. Monitor logs for denied packets to refine your policy and catch misconfigurations early.

Read the full guide: Implement Firewalls: A Step-by-Step Guide for Network Security

What to do and how to stay safe: Microsoft

• Verify if your organization runs Windows Internet Information Services and check its current configuration for exposure to untrusted networks.
• Monitor server logs for unusual request patterns or unexpected process executions that could indicate an exploitation attempt.
• Restrict access to web servers by using firewalls to block traffic from untrusted IP ranges and only allowing necessary connections.
• Prepare an incident response plan that includes steps for isolating compromised systems and investigating potential remote code execution.

Step-by-step guide: Automatic Updates Mistakes That Leave Systems Exposed

General security guidance from the RedTeam Monitor newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

What is the CVE ID for this Windows IIS vulnerability?

The CVE ID for this vulnerability is CVE-2026-70024.

How severe is this buffer overflow flaw according to the National Vulnerability Database?

The National Vulnerability Database rates CVE-2026-70024 as critical with a CVSS score of 9.8.

What type of attack does this vulnerability allow?

This vulnerability allows an unauthorized attacker to execute code over a network via a stack-based buffer overflow.