CVE-2013-0020 in Internet Explorer
Summary
by MITRE
Use-after-free vulnerability in Microsoft Internet Explorer 9 allows remote attackers to execute arbitrary code via a crafted web site that triggers access to a deleted object, aka "Internet Explorer CMarkup Use After Free Vulnerability."
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Analysis
by VulDB Data Team • 05/04/2021
The CVE-2013-0020 vulnerability represents a critical use-after-free flaw in Microsoft Internet Explorer 9 that enables remote code execution through malicious web content. This vulnerability specifically affects the CMarkup component within Internet Explorer, which handles markup processing for web documents. The flaw occurs when the browser processes crafted web pages that manipulate object references in memory, leading to situations where freed memory locations are accessed after being deallocated. This type of vulnerability falls under the CWE-416 category, which addresses use-after-free conditions, making it a well-documented and dangerous class of memory safety issues that have plagued software systems for decades.
The technical exploitation of this vulnerability involves creating a malicious web page that triggers the CMarkup component to process malformed markup elements. When Internet Explorer encounters such content, it may delete certain objects from memory while maintaining references to them, creating a scenario where subsequent operations attempt to access freed memory locations. This memory corruption can be leveraged by attackers to inject and execute arbitrary code with the privileges of the affected user. The vulnerability demonstrates the classic patterns of heap-based use-after-free exploits where attackers can manipulate memory layout to achieve code execution, often through techniques such as heap spraying or precise memory manipulation to overwrite critical data structures or function pointers.
The operational impact of this vulnerability is severe as it affects a widely deployed browser component that users interact with daily. Internet Explorer 9 was prevalent in corporate environments and among general users, making the attack surface substantial. Successful exploitation could result in complete system compromise, allowing attackers to install malware, steal sensitive data, or establish persistent access to affected systems. The vulnerability's remote nature means that users need only visit a malicious website to be compromised, making it particularly dangerous for targeted attacks. Organizations using Internet Explorer 9 were at significant risk, as the browser's memory management flaws could be exploited without requiring user interaction beyond visiting a compromised site, aligning with attack patterns documented in the MITRE ATT&CK framework under the 'Exploitation for Code Execution' tactic.
Microsoft addressed this vulnerability through security updates that corrected the memory management issues in the CMarkup component. The fix involved implementing proper object reference tracking and ensuring that memory deallocation occurred only after all references were properly invalidated. Security professionals recommended immediate patching of affected systems and advised organizations to implement network-based protections such as web application firewalls to block access to known malicious sites. The vulnerability highlighted the importance of memory safety in browser implementations and contributed to the industry-wide shift toward more secure programming practices and automated memory management techniques. Organizations should have implemented layered security approaches including browser hardening, user education, and network monitoring to protect against similar vulnerabilities, as documented in various cybersecurity frameworks that emphasize the need for defense-in-depth strategies against memory corruption exploits.