CVE-2011-1993 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 6 through 9 does not properly handle objects in memory, which allows remote attackers to execute arbitrary code by accessing a deleted object, aka "Scroll Event Remote Code Execution Vulnerability."
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Analysis
by VulDB Data Team • 03/19/2021
The vulnerability identified as CVE-2011-1993 represents a critical memory corruption issue affecting Microsoft Internet Explorer versions 6 through 9. This flaw manifests in the browser's improper handling of objects within memory management, creating a condition where attackers can manipulate the execution flow of the application. The vulnerability specifically occurs during scroll event processing, making it particularly dangerous as scroll events are among the most frequently triggered user interactions on web pages. The underlying technical issue stems from the browser's failure to properly validate object references after memory deallocation, allowing for the execution of malicious code through the exploitation of dangling pointers or use-after-free conditions.
This vulnerability operates at the intersection of multiple cybersecurity domains and aligns with CWE-476, which addresses null pointer dereference conditions, and CWE-122, which covers buffer overflow vulnerabilities. The attack vector leverages the browser's event handling mechanism where scroll events can trigger the execution of code on objects that have already been freed from memory. According to the ATT&CK framework, this vulnerability maps to T1203, which covers Exploitation for Client Execution, and T1059, representing Command and Scripting Interpreter. The remote code execution capability means that attackers can inject malicious payloads directly into the victim's browser session without requiring local system access, making this particularly dangerous in enterprise environments where users frequently browse untrusted websites.
The operational impact of CVE-2011-1993 extends beyond simple code execution, as it enables attackers to gain full control over affected systems. When a user visits a malicious webpage containing crafted JavaScript code, the vulnerability can be triggered through normal browsing behavior, making it extremely difficult to defend against through user education alone. The exploitation process typically involves creating a webpage that forces Internet Explorer to access a deleted object during scroll event processing, which then allows the attacker to execute arbitrary code with the privileges of the user running the browser. This makes the vulnerability particularly attractive to threat actors targeting enterprise users, as it can be easily weaponized through drive-by download attacks or malicious advertisements.
Mitigation strategies for CVE-2011-1993 must address both immediate protection and long-term remediation. Microsoft released security patches through Windows Update that fixed the memory handling issue in affected Internet Explorer versions, though organizations should prioritize immediate deployment of these updates. Additional protective measures include implementing browser hardening techniques such as disabling unnecessary ActiveX controls, enabling Internet Explorer's protected mode, and configuring security zones with appropriate restrictions. Network-level defenses such as web application firewalls and content filtering solutions can help detect and block malicious content that attempts to exploit this vulnerability. Organizations should also consider implementing browser isolation techniques and migrating users to more modern browsers that have better memory management and security features, as Internet Explorer versions 6 through 9 are no longer supported and lack modern security mitigations such as address space layout randomization and data execution prevention.