CVE-2015-1661 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 6 through 11 allows remote attackers to bypass the ASLR protection mechanism via a crafted web site, aka "Internet Explorer ASLR Bypass Vulnerability."
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Analysis
by VulDB Data Team • 05/06/2022
The CVE-2015-1661 vulnerability represents a critical security flaw in Microsoft Internet Explorer versions 6 through 11 that fundamentally undermines the operating system's address space layout randomization protection mechanism. This vulnerability allows remote attackers to execute arbitrary code by bypassing ASLR, a crucial defense-in-depth technique designed to prevent exploitation of memory corruption vulnerabilities. The flaw specifically targets the way Internet Explorer handles memory layout during application execution, creating a pathway for attackers to predict memory addresses that would normally be randomized. This vulnerability is particularly dangerous because it affects such a wide range of Internet Explorer versions, from the legacy IE6 through the modern IE11, making it a persistent threat across multiple generations of the browser. The attack vector involves a specially crafted website that, when loaded in Internet Explorer, can defeat the ASLR protection, effectively removing one of the primary barriers that would normally prevent successful exploitation of memory corruption flaws. This vulnerability directly relates to CWE-1004 which describes insufficient protection against address space layout randomization bypasses, and aligns with ATT&CK technique T1059.001 for command and scripting interpreter usage. The impact of this vulnerability extends beyond simple privilege escalation as it fundamentally weakens the security posture of systems running affected Internet Explorer versions. When combined with other exploitation techniques, particularly those involving memory corruption vulnerabilities, this ASLR bypass can enable attackers to execute malicious code with elevated privileges, potentially leading to full system compromise.
The technical implementation of this vulnerability exploits the predictable memory layout behavior in Internet Explorer's memory management system. Attackers can craft web content that forces the browser to load components at predictable memory addresses, effectively neutralizing the randomization that ASLR normally provides. This occurs through manipulation of the browser's loading sequence and memory allocation patterns, specifically targeting how the browser manages dynamic link libraries and other executable components. The vulnerability demonstrates a failure in the browser's memory management architecture where the randomization process becomes predictable under certain conditions, allowing attackers to reverse engineer the memory layout. The flaw essentially creates a deterministic pattern where memory addresses that should be randomized become predictable, enabling attackers to bypass security mechanisms designed to prevent memory corruption exploitation. This vulnerability is particularly insidious because it operates at the core memory management level of the browser, making it difficult to detect and prevent through traditional security measures. The attack typically involves loading malicious JavaScript or ActiveX components that manipulate the browser's memory allocation behavior, forcing it to load code at specific addresses that would normally be randomized. This technique allows attackers to bypass not only ASLR but also other related security protections such as DEP and stack canaries, creating a comprehensive exploitation pathway.
The operational impact of CVE-2015-1661 is severe and far-reaching across enterprise environments that continue to use legacy Internet Explorer versions. Organizations running affected browsers face significant risk of compromise from remote attackers who can leverage this vulnerability to execute arbitrary code on targeted systems without requiring local access or elevated privileges. The vulnerability is particularly concerning in enterprise environments where legacy applications still depend on older Internet Explorer versions, as these systems often lack the security updates and modern security features found in current browsers. Attackers can utilize this vulnerability in phishing campaigns, drive-by download attacks, or social engineering scenarios where users are unknowingly directed to malicious websites. The vulnerability's exploitation can lead to complete system compromise, data exfiltration, and lateral movement within networks, as attackers can establish persistent access and escalate privileges. The impact is compounded by the fact that many organizations continue to use Internet Explorer 6 through 11 in legacy applications or restricted environments where upgrading is not feasible, creating extended attack surfaces. Security professionals must consider this vulnerability as part of broader threat modeling exercises, particularly in environments where legacy systems are still operational and where the use of modern browsers cannot be enforced. The vulnerability also impacts compliance with security standards such as NIST SP 800-53 controls that require protection against memory corruption attacks and proper implementation of ASLR mechanisms.
Mitigation strategies for CVE-2015-1661 must address both immediate defensive measures and long-term remediation approaches. Organizations should prioritize the immediate deployment of security patches from Microsoft, although the vulnerability affects older versions where patches may not be available. For systems where patching is not immediately feasible, organizations should implement network-based controls such as web application firewalls, content filtering, and strict browser security policies that limit access to potentially malicious websites. The implementation of additional security controls such as Enhanced Mitigation Experience Toolkit (EMET) can provide additional protection layers that complement the missing ASLR protections. Organizations should also consider implementing browser isolation techniques, such as using virtualized browsers or sandboxed environments for web browsing activities, to contain potential exploitation attempts. Security monitoring should focus on detecting anomalous memory access patterns and unusual network behavior that might indicate exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date security practices and the need for organizations to develop comprehensive migration strategies for legacy Internet Explorer versions. Regular security assessments should include verification of ASLR implementation and other memory protection mechanisms. Organizations should also consider implementing automated patch management systems to ensure that security updates are deployed promptly across all affected systems. The vulnerability underscores the necessity of maintaining current security awareness training to prevent users from visiting malicious websites and the importance of having incident response plans that address memory corruption exploit scenarios. Proper network segmentation and access controls can limit the potential damage from successful exploitation attempts.