Microsoft Office users are under attack today from a zero-day vulnerability that is not set to be patched until April 11. Security firm McAfee first publicly posted about the new zero-day vulnerability in Microsoft Word files on April 7, with security firm FireEye following with its own disclosure a day later on April 8.
At this point, it's not entirely clear how many users may have already been exploited by the zero-day attack.
"We plan to address this through an update on Tuesday, April 11, and customers who have updates enabled will be protected automatically," Microsoft wrote in a statement sent to eWEEK. "Meanwhile, we encourage customers to practice safe computing habits online, including exercising caution before opening unknown files and not downloading content from untrusted sources to avoid this type of issue."
The issue, as described by McAfee and FireEye is found in Microsoft Office's Word application, specifically linked to Rich Text Format (RTF) documents. The vulnerability is present in all versions of Microsoft Office, including the latest Office 2016 edition running on the Windows 10 operating system. The actual vulnerability is a flaw in the Windows Object Linking and Embedding (OLE) component that enables content to be linked inside of documents.
"The exploit connects to a remote server (controlled by the attacker), downloads a file that contains HTML application content, and executes it as an .hta file," McAfee explained in its disclosure.
McAfee added that due to the fact that the .hta file is executable, an attacker is able to gain full code execution on the victim's machine. Additionally, McAfee warns that the attack can potentially enable attackers to bypass various memory-based mitigations that are present in Microsoft Windows.
For it's part, FireEye reported that it has seen the vulnerability used in attacks, deploying various malicious payloads from different well-known malware families. FireEye specifically noted that an embedded OLE2link object is used in the attack, triggering the malicious .hta file, which then executes the malicious payload. FireEye explains in its disclosure that the malicious script ends up terminating the winword.exe (Word application) process, in turn loading a decoy document.
"The original winword.exe process is terminated in order to hide a user prompt generated by the OLE2link," FireEye warns.
According to McAfee, the earliest attacks that it has seen for the new OLE Word attack data back to January 2017, though Microsoft has had various issues with OLE in the past as well. Back in 2014, Microsoft users were also at risk from an OLE related vulnerability, that was being actively exploited by attackers. The 2014 OLE vulnerabilities were being exploited as part of a vulnerability known as Sandworm that targeted NATO and the European Union (EU).