RESEARCHERS WARNED LAST weekend that a flaw in Microsoft’s Support Diagnostic Tool could be exploited using malicious Word documents to remotely take control of target devices. Microsoft released guidance on Monday, including temporary defense measures. By Tuesday, the United States Cybersecurity and Infrastructure Security Agency had warned that “a remote, unauthenticated attacker could exploit this vulnerability,” known as Follina, “to take control of an affected system.” But Microsoft would not say when or whether a patch is coming for the vulnerability, even though the company acknowledged that the flaw was being actively exploited by attackers in the wild. And the company still had no comment about the possibility of a patch when asked by WIRED yesterday.
The Follina vulnerability in a Windows support tool can be easily exploited by a specially crafted Word document. The lure is outfitted with a remote template that can retrieve a malicious HTML file and ultimately allow an attacker to execute Powershell commands within Windows. Researchers note that they would describe the bug as a “zero-day,” or previously unknown vulnerability, but Microsoft has not classified it as such.
“After public knowledge of the exploit grew, we began seeing an immediate response from a variety of attackers beginning to use it,” says Tom Hegel, senior threat researcher at security firm SentinelOne. He adds that while attackers have primarily been observed exploiting the flaw through malicious documents thus far, researchers have discovered other methods as well, including the manipulation of HTML content in network traffic.
“While the malicious document approach is highly concerning, the less documented methods by which the exploit can be triggered are troubling until patched,” Hegel says. “I would expect opportunistic and targeted threat actors to use this vulnerability in a variety of ways when the option is available—it’s just too easy.”
The vulnerability is present in all supported versions of Windows and can be exploited through Microsoft Office 365, Office 2013 through 2019, Office 2021, and Office ProPlus. Microsoft’s main proposed mitigation involves disabling a specific protocol within Support Diagnostic Tool and using Microsoft Defender Antivirus to monitor for and block exploitation.
But incident responders say that more action is needed, given how easy it is to exploit the vulnerability and how much malicious activity is being detected.