CVE-2013-2551

What is Microsoft Internet Explorer?

Microsoft Internet Explorer was the dominant desktop browser through the 2000s and 2010s. IE's DOM (Document Object Model) engine manages JavaScript object lifetimes in coordination with the HTML rendering engine. Use-after-free vulnerabilities arise when a JavaScript reference to a DOM object outlives the object's internal memory allocation, allowing IE to read freed memory the next time the dangling reference is accessed during rendering or event handling.

Overview

CVE-2013-2551 is a use-after-free vulnerability (CWE-416) in Microsoft Internet Explorer affecting IE versions 6 through 10. The vulnerability occurs when IE accesses a deleted DOM object via a dangling reference during crafted HTML rendering — specifically related to undo/redo operation tracking objects. Exploitation allows remote code execution in the context of the current user. CISA confirmed ransomware use of this vulnerability.

Microsoft patched CVE-2013-2551 in MS13-037 (May 2013 Patch Tuesday).

Affected Versions

Technical Details

The vulnerability involves IE's internal undo/redo tracking mechanism. IE maintains undo unit objects (CParentUndoUnit and related classes) to track document editing operations. When JavaScript manipulates the DOM in a specific way that causes these internal objects to be freed while references to them remain active in the rendering pipeline, IE subsequently accesses the freed memory — triggering a use-after-free condition (CWE-416).

Exploitation method: Classic IE use-after-free exploitation:

1. JavaScript heap spray fills freed memory with attacker-controlled content before the dangling pointer is dereferenced
2. The freed pointer is accessed during rendering/event processing, treating heap spray content as a live object
3. The attacker's data includes a fake vtable pointer redirecting a virtual function call to shellcode or ROP chains

Broad version coverage: Affecting IE 6 through IE 10 makes this high-value — IE's installed base across Windows XP, Vista, 7, and 8 was enormous in 2013, and many organizations ran IE 6 or 8 on XP due to legacy application dependencies.

Exploit kit integration: The vulnerability appeared in exploit kits including Blackhole, giving it wide deployment against consumer and enterprise targets without requiring any targeting sophistication.

Discovery

CVE-2013-2551 was first published as a known vulnerability in March 2013, approximately two months before Microsoft released the patch in May 2013. This gap means the vulnerability was exposed to active exploitation as an effectively unpatched flaw for the final weeks of that window.

Exploitation Context

CISA confirmed ransomware delivery via CVE-2013-2551. The vulnerability's broad IE version coverage and exploit kit adoption made it a standard component in drive-by download campaigns in 2013. Ransomware families of the era — including CryptoLocker predecessors and police/scareware ransomware — used exploit kit infrastructure to compromise machines via browser vulnerabilities, then install their payloads.

Remediation

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

1. Uninstall or disable Internet Explorer — replace with Microsoft Edge
2. For historical remediation: MS13-037 (May 2013) patches this vulnerability
3. Remove IE from default application associations via Group Policy
4. Audit legacy line-of-business applications requiring Internet Explorer — migrate to Edge with IE compatibility mode