CVE-2014-8967 in Internet Explorer
Summary
by MITRE
Use-after-free vulnerability in Microsoft Internet Explorer allows remote attackers to execute arbitrary code via a crafted HTML document in conjunction with a Cascading Style Sheets (CSS) token sequence specifying the run-in value for the display property, leading to improper CElement reference counting.
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Analysis
by VulDB Data Team • 02/27/2022
The CVE-2014-8967 vulnerability represents a critical use-after-free flaw in Microsoft Internet Explorer that demonstrates the dangerous consequences of improper memory management in web browsers. This vulnerability specifically targets the rendering engine's handling of CSS properties, particularly the display property with the run-in value, creating a scenario where freed memory can be accessed and manipulated by malicious actors. The flaw occurs when Internet Explorer processes a crafted HTML document containing specific CSS token sequences that trigger incorrect reference counting mechanisms within the CElement class structure. This improper reference counting leads to memory that has been deallocated being accessed again, creating a condition where attackers can inject and execute arbitrary code on vulnerable systems.
The technical exploitation of this vulnerability requires a sophisticated understanding of Internet Explorer's internal memory management systems and browser rendering processes. When the browser encounters a CSS declaration with display: run-in, it triggers a specific code path that involves the CElement class reference counting mechanism. The flaw manifests as a race condition or improper memory deallocation where the reference counter does not accurately reflect the actual usage of memory objects, allowing freed memory locations to be reused before proper cleanup occurs. This creates a predictable memory layout that attackers can manipulate to overwrite critical memory regions, ultimately leading to code execution privileges. The vulnerability operates at the intersection of web rendering and memory management, making it particularly dangerous as it combines the complexity of CSS parsing with the fundamental security principles of memory safety.
The operational impact of CVE-2014-8967 extends beyond simple code execution to represent a comprehensive compromise of system security in enterprise and consumer environments. Attackers leveraging this vulnerability can gain full control over affected systems, potentially leading to data theft, privilege escalation, and persistent backdoor access. The remote nature of the attack means that victims need only visit a malicious website or open a crafted email attachment containing the malicious HTML content. This vulnerability particularly affects organizations running older versions of Internet Explorer, as Microsoft had not yet patched the issue when it was disclosed, creating a window of opportunity for widespread exploitation. The attack vector demonstrates how seemingly innocuous CSS properties can be weaponized to create serious security breaches, highlighting the importance of comprehensive input validation and memory safety practices in web browser implementations.
Mitigation strategies for CVE-2014-8967 must address both immediate remediation and long-term architectural improvements in browser security. The primary solution involves applying Microsoft's security patches and updates that correct the reference counting mechanisms within Internet Explorer's rendering engine. Organizations should also implement network-level protections such as web application firewalls and content filtering systems that can detect and block malicious CSS sequences. Browser hardening techniques including disabling unnecessary CSS features and implementing strict memory protection mechanisms can reduce the attack surface. From a defensive perspective, this vulnerability aligns with CWE-416 which addresses use-after-free conditions, and it maps to ATT&CK technique T1059.001 for command and scripting interpreter and T1071.001 for application layer protocol. The vulnerability underscores the necessity of robust memory safety practices and proper input validation in web browser implementations, as well as the importance of regular security updates and vulnerability management processes to prevent exploitation of such critical flaws.