CVE-2013-3893

What is Microsoft Internet Explorer?

Microsoft Internet Explorer was the dominant enterprise browser through the 2010s, with especially high market share in Japan's corporate and government sectors. IE's mouse handling subsystem includes SetMouseCapture — an internal mechanism that redirects all mouse events to a specific element until capture is released. When an element captures mouse input and is subsequently deleted from the DOM before capture is released, IE's mouse dispatch code holds a dangling pointer to the freed element.

Overview

CVE-2013-3893 is a use-after-free vulnerability (CWE-399) in Microsoft Internet Explorer involving the SetMouseCapture API. When JavaScript manipulates the DOM to delete a mouse-capturing element without releasing mouse capture, IE's internal event dispatch code retains a dangling pointer to the freed element. Accessing the freed element during subsequent mouse event processing triggers the use-after-free, enabling arbitrary code execution. This was a zero-day exploited in Operation DeputyDog — a targeted attack campaign against Japanese government, technology, and defense organizations.

Microsoft released out-of-band emergency patch MS13-080 on October 8, 2013.

Affected Versions

Technical Details

Internet Explorer's mouse capture mechanism routes all mouse events to a designated element after SetMouseCapture() is called. IE maintains an internal pointer to the capturing element. The use-after-free occurs when:

1. JavaScript calls SetMouseCapture() on a DOM element, registering it to receive all mouse events
2. JavaScript subsequently removes the same element from the DOM without explicitly releasing mouse capture
3. IE frees the element's internal C++ object as part of DOM cleanup
4. The mouse capture pointer in IE's event dispatch system still points to the freed memory (a dangling pointer)
5. When the user moves the mouse or triggers another mouse event, IE dispatches it to the freed element via the dangling pointer

An attacker who controls the heap (via JavaScript heap spray) can fill the freed memory with attacker-controlled data before step 5, redirecting execution when IE calls a virtual method on the dangling pointer.

Zero-day exploitation context: Microsoft acknowledged the unpatched zero-day via Security Advisory 2887505 on September 17, 2013 — the same day FireEye published its Operation DeputyDog report. The 21-day gap between public disclosure and the MS13-080 patch left IE 8–10 users exposed to a known, actively exploited zero-day with publicly available details.

Discovery

Discovered by FireEye, which identified the zero-day in the context of water-holing attacks against Japanese organizations in September 2013. FireEye published the Operation DeputyDog report on September 17, 2013, prompting Microsoft's same-day acknowledgment via security advisory.

Exploitation Context

CISA added this to the KEV catalog in August 2025, confirming historical exploitation. Operation DeputyDog was a coordinated APT campaign — assessed as Chinese state-sponsored — targeting Japanese organizations. Characteristics:

• Water-holing: Attackers compromised legitimate Japanese websites frequented by target organizations (technology companies, government contractors, defense industry)
• Selective targeting: The exploit was served specifically to IE 8, 9, and 10 users, matching the browser distribution of Japanese corporate environments
• Payload: Delivered a customized variant of the HiKit RAT (remote access trojan), designed for persistence and data exfiltration

The fact that CISA added this to KEV in 2025 — over a decade after the patch — indicates continued exploitation risk against organizations running outdated IE versions or unpatched Windows systems.

Remediation

Internet Explorer reached end-of-life on June 15, 2022. Organizations should:

1. Uninstall or disable Internet Explorer — replace with Microsoft Edge immediately
2. For historical remediation: MS13-080 (October 2013) patches CVE-2013-3893 for IE 8, 9, and 10
3. Remove IE from default application associations via Group Policy and disable the iexplore.exe executable
4. Audit any remaining systems with Internet Explorer installed — these systems may be running other long-unpatched vulnerabilities
5. Implement network controls that block access from hosts running Internet Explorer to sensitive internal resources