Chinese Hackers Begin Exploiting Latest Microsoft Office Zero-Day Vulnerability

An advanced persistent threat (APT) actor aligned with Chinese state interests has been observed weaponizing the new zero-day flaw in Microsoft Office to achieve code execution on affected systems.

"TA413 CN APT spotted [in-the-wild] exploiting the Follina zero-day using URLs to deliver ZIP archives which contain Word Documents that use the technique," enterprise security firm Proofpoint said in a tweet.

"Campaigns impersonate the 'Women Empowerments Desk' of the Central Tibetan Administration and use the domain tibet-gov.web[.]app."

TA413 is best known for its campaigns aimed at the Tibetan diaspora to deliver implants such as Exile RAT and Sepulcher as well as a rogue Firefox browser extension dubbed FriarFox.

The high-severity security flaw, dubbed Follina and tracked as CVE-2022-30190 (CVSS score: 7.8), relates to a case of remote code execution that abuses the "ms-msdt:" protocol URI scheme to execute arbitrary code.

Specifically, the attack makes it possible for threat actors to circumvent Protected View safeguards for suspicious files by simply changing the document to a Rich Text Format (RTF) file, thereby allowing the injected code to be run without even opening the document via the Preview Pane in Windows File Explorer.

While the bug gained widespread attention last week, evidence points to active exploitation of the diagnostic tool flaw in real-world attacks targeting Russian users over a month ago on April 12, 2022, when it was disclosed to Microsoft.

The company, however, did not deem it a security issue and closed the vulnerability submission report, citing reasons that the MSDT utility requires a passkey provided by a support technician before it can execute payloads.

The vulnerability exists in all currently supported Windows versions and can be exploited via Microsoft Office versions Office 2013 through Office 21 and Office Professional Plus editions.

"This elegant attack is designed to bypass security products and fly under the radar by leveraging Microsoft Office's remote template feature and the ms-msdt protocol to execute malicious code, all without the need for macros," Malwarebytes' Jerome Segura noted.

Although there is no official patch available at this point, Microsoft has recommended disabling the MSDT URL protocol to prevent the attack vector. Additionally, it's been advised to turn off the Preview Pane in File Explorer.

"What makes 'Follina' stand out is that this exploit does not take advantage of Office macros and, therefore, it works even in environments where macros have been disabled entirely," Nikolas Cemerikic of Immersive Labs said.

"All that's required for the exploit to take effect is for a user to open and view the Word document, or to view a preview of the document using the Windows Explorer Preview Pane. Since the latter does not require Word to launch fully, this effectively becomes a zero-click attack."

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