Source: secure@microsoft.com
Use-after-free vulnerability in Microsoft Internet Explorer 6 through 8 allows remote attackers to execute arbitrary code via a crafted web site that triggers access to an object that (1) was not properly allocated or (2) is deleted, as demonstrated by a CDwnBindInfo object, and exploited in the wild in December 2012.
Microsoft Internet Explorer 6-8 is vulnerable to a critical use-after-free vulnerability, allowing remote attackers to execute arbitrary code on a victim's system. This vulnerability, actively exploited in the wild, enables attackers to gain complete control of a compromised machine through malicious websites.
Step 1: Malicious Website Delivery: The attacker crafts a malicious website or compromises a legitimate one to host the exploit code.
Step 2: Object Instantiation and Manipulation: The website uses JavaScript to instantiate and manipulate specific objects, including the vulnerable CDwnBindInfo object.
Step 3: Object Deletion (Freeing): The JavaScript code triggers the deletion of the CDwnBindInfo object, freeing the memory associated with it.
Step 4: Use-After-Free Trigger: The exploit code then attempts to access the freed CDwnBindInfo object, triggering the use-after-free vulnerability.
Step 5: Memory Corruption: The attacker's crafted code overwrites memory, potentially including function pointers or other critical data structures.
Step 6: Code Execution: When the corrupted data is used, the attacker's malicious code is executed, granting them control of the victim's system.
The vulnerability stems from a flaw in how Internet Explorer handles the CDwnBindInfo object. Specifically, the code fails to properly manage the object's lifecycle, leading to a use-after-free condition. When a crafted website triggers a sequence of events, the object is accessed after it has been freed from memory. This allows an attacker to overwrite memory with malicious code, leading to arbitrary code execution. The root cause is a lack of proper memory management and insufficient checks to prevent access to freed memory. The attacker can control the memory layout and overwrite critical data structures, leading to code execution in the context of the user.
This vulnerability was exploited by various threat actors. While specific APT attribution is difficult without further analysis, the widespread exploitation suggests it was used by multiple groups. This vulnerability is likely included in CISA's Known Exploited Vulnerabilities (KEV) catalog.
Network traffic analysis looking for suspicious HTTP requests to websites known to host exploits.
Web server logs analysis for unusual user-agent strings or requests associated with exploit attempts.
Endpoint detection and response (EDR) systems looking for suspicious process creation or memory manipulation activities within Internet Explorer (iexplore.exe).
Memory forensics on compromised systems to identify the presence of malicious code injected into Internet Explorer's process space.
Signature-based detection using intrusion detection systems (IDS) and intrusion prevention systems (IPS) to identify known exploit patterns.
Behavioral analysis to identify unusual activity, such as unexpected network connections or the execution of shellcode.
Apply the latest security updates from Microsoft to patch the vulnerability. This is the primary and most effective remediation step.
Disable or uninstall Internet Explorer if it is not required for business operations. Consider using alternative web browsers.
Implement a strong web content filtering policy to block access to malicious websites.
Educate users about the dangers of clicking on suspicious links or opening attachments from untrusted sources.
Enable Enhanced Mitigation Experience Toolkit (EMET) or similar security tools to provide additional protection against exploitation (though EMET is deprecated, its principles are still relevant).
Implement a robust patch management process to ensure that security updates are applied promptly.
Regularly scan systems for vulnerabilities and monitor for suspicious activity.