CVE-2019-0752: Microsoft Internet Explorer Type Confusion Vulnerability

CVE-2019-0752 is a type confusion vulnerability in Microsoft Internet Explorer that can lead to remote code execution. It arises when the scripting engine mishandles objects in memory, allowing an attacker who can entice a user to open crafted web content to run code in the context of the logged-on user. Because the flaw has been associated with ransomware activity, organizations still running Internet Explorer should treat it as a priority for inventory and remediation.

Public detail is limited to the CISA summary and the stated CWE; exact affected builds, exploit mechanics, and scoring must be confirmed against the vendor advisory. The required action is to apply updates per vendor instructions.

How it works

The weakness is classified as CWE-843 (Access of Resource Using Incompatible Type, commonly called type confusion). In a type-confusion bug the engine treats a memory object as one type when it is actually another. When the Internet Explorer scripting engine performs operations on that object, the mismatch can corrupt memory layout or control flow.

An attacker abuses this by delivering specially crafted script or markup that the browser’s scripting engine processes. Successful exploitation can achieve remote code execution with the privileges of the user running the browser. No further exploit specifics are provided in the available facts; defenders should rely on the vendor advisory for any additional technical description rather than assuming particular primitives or chains.

Am I affected? How to find it in your systems

Internet Explorer has historically been present on Windows desktops and servers, often as a default or legacy component even when another browser is preferred. It may still appear in enterprise images, kiosks, older line-of-business applications that embed the Trident/MSHTML engine, or systems where IE mode or compatibility features remain enabled.

• Inventory Windows endpoints and servers for the presence of Internet Explorer or the underlying scripting/MSHTML components via software inventory tools, configuration-management databases, or scripts that query installed features and browser binaries.
• Identify any applications or internal sites that explicitly require or launch Internet Explorer.
• Confirm which versions or security updates are installed against the vendor advisory; do not assume a build is safe without that check.
• Review web proxy, DNS, and endpoint logs for unusual IE process launches, crashes of iexplore.exe or related scripting hosts, or traffic to untrusted sites that could deliver exploit content. Telemetry indicating memory-corruption crashes in the scripting engine may also warrant investigation, though such signs are not unique to this CVE.

How to remediate

Patch first. Apply the updates Microsoft released for this vulnerability exactly as directed in the vendor advisory and follow the CISA required action: apply updates per vendor instructions. After patching, verify the update is present across the estate through your normal patch-compliance reporting.

Beyond the patch, harden the browser attack surface for this class of flaw:

• Reduce or eliminate reliance on Internet Explorer; migrate users and applications to a modern, supported browser.
• Enforce least privilege so that even successful code execution runs with limited rights.
• Keep the operating system and related components current so that secondary mitigations (ASLR, DEP, CFG, and similar) remain effective.
• Disable or restrict unnecessary Active Scripting and legacy ActiveX where business needs allow.

If you can't patch immediately

When immediate patching is not possible, apply compensating controls to lower likelihood and impact until the update can be deployed:

• Network segmentation and application allow-listing to limit which systems can reach untrusted web content and which processes Internet Explorer can launch.
• Virtual patching or WAF/proxy rules that block or detonate known malicious patterns targeting IE scripting, while recognizing that signature coverage for type-confusion exploits is imperfect.
• Disable the affected feature or the browser itself where feasible—for example, by removing IE shortcuts, restricting launch via software restriction or AppLocker policies, or forcing use of a different browser.
• Heighten monitoring: alert on IE process creation from Office or email clients, unexpected child processes, and outbound connections from iexplore.exe to rare destinations. Retain crash dumps for later analysis.

These measures reduce risk but do not replace the vendor update.

If your data may have been exposed

Actively exploited vulnerabilities, including those known to be used with ransomware, frequently precede broader compromise and data theft. If you have reason to believe systems were exposed before patching, follow your incident-response process: isolate affected hosts, preserve evidence, and assess whether credentials or data left the environment. As one additional check, you can run a free exposure scan of your email addresses against known breach data sets to see whether associated accounts appear in prior incidents.