CVE-2017-0037

What Are Microsoft Edge and Internet Explorer?

Microsoft Edge (legacy EdgeHTML-based) and Internet Explorer are Microsoft's Windows web browsers. Both browsers use the mshtml.dll rendering engine (Trident) for HTML/CSS parsing and layout, and both execute JavaScript via their respective engines (Chakra for Edge, JScript for IE). The mshtml.dll rendering engine — shared between IE and legacy Edge — has been a persistent source of type confusion and memory corruption vulnerabilities due to the complexity of processing HTML, CSS, JavaScript DOM interactions, and the legacy compatibility requirements of a codebase that has evolved for decades.

Overview

CVE-2017-0037 is a type confusion vulnerability in the mshtml.dll rendering engine shared by Microsoft Edge and Internet Explorer that allows remote code execution when a user visits a malicious web page. The mshtml.dll engine maintains internal type information about DOM objects; this vulnerability allows a specially crafted HTML/script combination to cause the engine to access a DOM object using incorrect type semantics, enabling arbitrary read/write in the browser process and code execution. Patched in MS17-007 (March 14, 2017). CISA added CVE-2017-0037 to the KEV catalog in March 2022.

Affected Versions

Technical Details

Root Cause: mshtml.dll Type Confusion

CVE-2017-0037 is a type confusion vulnerability (CWE-843) in mshtml.dll — the rendering engine that processes HTML documents and exposes the DOM to JavaScript in Internet Explorer and legacy Edge. The rendering engine manages many internal object types for DOM elements (HTMLElement, HTMLInputElement, HTMLAnchorElement, etc.) and maintains type metadata used for type-safe method dispatch and property access.

Type confusion mechanism: A type confusion vulnerability in a rendering engine occurs when the engine treats a DOM object as a different type than it actually is:

1. Attacker crafts a web page — specific HTML/JavaScript interactions cause the rendering engine to maintain inconsistent type information for a DOM object
2. Type metadata is corrupted or inconsistent — the rendering engine stores a reference to the object with incorrect type information
3. Wrong-type access — when the object is accessed as the wrong type, method dispatch or property access interprets the object's data fields according to the wrong type layout
4. Read/write primitive — this type mismatch provides an attacker with the ability to read/write memory at attacker-controlled offsets from the object base address
5. Code execution — the read/write primitive is used to overwrite a function pointer or code pointer within the browser process, redirecting execution

AC:H — High Complexity

The CVSS AC:H (Attack Complexity: High) indicates exploitation requires specific conditions beyond simply visiting a malicious page — likely specific browser version or state, a particular scripting interaction sequence, or a race condition in the rendering engine. Despite AC:H, the vulnerability was observed in active exploitation, indicating reliable exploitation is achievable with sufficient engineering.

Attack Characteristics

Discovery

Disclosed by an external researcher via coordinated disclosure; patched in MS17-007 (March 2017 Patch Tuesday) alongside other Edge and Internet Explorer scripting engine vulnerabilities.

Exploitation Context

• mshtml.dll as recurring target: The mshtml.dll rendering engine, used by both IE and legacy Edge, has been one of the most exploited Windows components for browser-based code execution; its legacy codebase, complex object type system, and compatibility requirements create a large attack surface
• Exploit kit incorporation: mshtml.dll type confusion vulnerabilities were systematically incorporated into exploit kits for drive-by malware delivery; RIG and Magnitude exploit kits updated to include MS17-007-fixed vulnerabilities rapidly after disclosure
• Enterprise IE exposure: Internet Explorer remained widely deployed in enterprise environments for intranet compatibility through 2017; CVE-2017-0037 was exploitable against enterprise users forced to use IE for internal web applications
• CISA KEV (2022): Added March 2022 reflecting documented exploitation of this mshtml.dll type confusion in active attack campaigns

Remediation

1. Apply MS17-007 — install the March 2017 Edge/Internet Explorer security update via Windows Update or WSUS. All subsequent Windows cumulative updates include this fix.

2. Migrate from Internet Explorer — Microsoft ended Internet Explorer 11 desktop support on June 15, 2022; migrate to Microsoft Edge (Chromium), Chrome, or Firefox to eliminate the legacy mshtml.dll attack surface.

3. Migrate from legacy Edge (EdgeHTML) — the legacy EdgeHTML-based Edge was replaced by Chromium-based Edge in 2020; update to current Chromium-based Edge for a modern, actively maintained browser.

4. Keep Windows fully updated — cumulative updates include all prior IE/Edge security patches.