Exploits for nasty Internet Explorer bug found on hacking forums

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In addition to sharing working exploits, threat actors are not sharing tutorials to help others fabricate their own attacks that make use of the recently discovered zero-day vulnerability (opens in new tab) in Internet Explorer (opens in new tab)’s browser engine Trident, also known as MSHTML, according to reports.

Microsoft disclosed the vulnerability, tracked as CVE-2021-40444, last week saying that it could be weaponized through malicious documents with ActiveX content to execute commands on a victim's computer remotely.

Soon after Microsoft’s disclosure, security researchers were able to spot documents (opens in new tab) on the internet with ActiveX content designed specifically to take advantage of CVE-2021-40444.

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BleepingComputer now reports that threat actors have started circulating guides and information regarding the vulnerability on underground hacking forums to help other malicious users craft exploits based on CVE-2021-40444.

No cure, only mitigations

Although software companies don’t disclose a vulnerability, until it has been fixed, Microsoft’s hand was forced after security vendors EXPMON and Mandiant both spotted the vulnerability being exploited. 

In response, Microsoft decided to disclose the vulnerability and shared mitigations (opens in new tab), which involve blocking ActiveX controls and Microsoft Office (opens in new tab) document previews in Windows Explorer, to defang the exploit, even as the software giant works to create a patch to plug the vulnerability. 

However, researchers have since been able to modify the exploit (opens in new tab) not to use ActiveX, effectively bypassing Microsoft's mitigations. Threat actors reportedly had already discovered this workaround, and used it to create more spurious documents and instructions. 

The information is reportedly simple to follow and enables anyone to create their own working version of the CVE-2021-40444 exploit.

The good news however is that security programs (opens in new tab) such as Microsoft Defender (opens in new tab) have been equipped to detect and flag such malicious documents, which is the best users can hope for in the absence of an official fix.

Via BleepingComputer (opens in new tab)

Mayank Sharma

With almost two decades of writing and reporting on Linux, Mayank Sharma would like everyone to think he’s TechRadar Pro’s expert on the topic. Of course, he’s just as interested in other computing topics, particularly cybersecurity, cloud, containers, and coding.