The U.S. Computer Emergency Readiness Team (CERT) said today that a vulnerability in Internet Explorer is being actively exploited, and is recommending that people use browsers other than IE until Microsoft issues a fix.
The vulnerability affects IE 6 through 11 and “could lead to the complete compromise of an affected system,” according to CERT.
“By convincing a user to view a specially crafted HTML document (e.g., a Web page or an HTML email message or attachment), an attacker may be able to execute arbitrary code,” CERT said.
CERT is also recommending that people use a Microsoft mitigation toolkit and to follow the company’s advice on workarounds.
Microsoft said the attacks are limited and targeted, and that it is investigating.
In a security advisory issued Saturday, the company said:
The vulnerability is a remote code execution vulnerability. The vulnerability exists in the way that Internet Explorer accesses an object in memory that has been deleted or has not been properly allocated. The vulnerability may corrupt memory in a way that could allow an attacker to execute arbitrary code in the context of the current user within Internet Explorer. An attacker could host a specially crafted website that is designed to exploit this vulnerability through Internet Explorer and then convince a user to view the website.
Microsoft did not give an estimate for when a fix would be available but did say: “On completion of this investigation, Microsoft will take the appropriate action to protect our customers, which may include providing a solution through our monthly security update release process, or an out-of-cycle security update, depending on customer needs.”
(Any update that is issued will not include Windows XP, for which Microsoft ended support on April 8. “Microsoft no longer provides security updates for this operating system. Our advice to customers is to migrate to a modern OS, like Windows 7 or Windows 8.1,” the company said in a statement.)
Microsoft, in a blog post on the issue, advised the following measures in the meantime:
Our initial investigation has revealed that Enhanced Protected Mode, on by default for the modern browsing experience in Internet Explorer 10 and Internet Explorer 11, as well as Enhanced Mitigation Experience Toolkit (EMET) 4.1 and EMET 5.0 Technical Preview, will help protect against this potential risk. We also encourage you to follow the “Protect Your Computer” guidance of enabling a firewall, applying all software updates and installing anti-virus and anti-spyware software. Additionally, we encourage everyone to exercise caution when visiting websites and avoid clicking suspicious links, or opening email messages from unfamiliar senders.