Microsoft on Monday published guidance for a newly discovered zero-day security flaw in its Office productivity suite that could be exploited to achieve code execution on affected systems.
The weakness, now assigned the identifier CVE-2022-30190, is rated 7.8 out of 10 for severity on the CVSS vulnerability scoring system. Microsoft Office versions Office 2013, Office 2016, Office 2019, and Office 2021, as well as Professional Plus editions, are impacted.
"To help protect customers, we've published CVE-2022-30190 and additional guidance here," a Microsoft spokesperson told The Hacker News in an emailed statement.
The Follina vulnerability, which came to light late last week, involved a real-world exploit that leveraged the shortcoming in a weaponized Word document to execute arbitrary PowerShell code by making use of the "ms-msdt:" URI scheme. The sample was uploaded to VirusTotal from Belarus.
But first signs of exploitation of the flaw date back to April 12, 2022, when a second sample was uploaded to the malware database. This artifact is believed to have targeted users in Russia with a malicious Word document ("приглашение на интервью.doc") that masqueraded as an interview invitation with Sputnik Radio.
"A remote code execution vulnerability exists when MSDT is called using the URL protocol from a calling application such as Word," Microsoft said in an advisory for CVE-2022-30190.
"An attacker who successfully exploits this vulnerability can run arbitrary code with the privileges of the calling application. The attacker can then install programs, view, change, or delete data, or create new accounts in the context allowed by the user's rights."
The tech giant credited crazyman, a member of the Shadow Chaser Group, for reporting the flaw on April 12, coinciding with the discovery of the in-the-wild exploit targeting Russian users, indicating the company had been already aware of the vulnerability.
Indeed, according to screenshots shared by the researcher on Twitter, Microsoft closed the vulnerability submission report on April 21, 2022 stating "the issue has been fixed," while also dismissing the flaw as "not a security issue" since it requires a passkey provided by a support technician when starting the diagnostic tool.
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Besides releasing detection rules for Microsoft Defender for Endpoint, the Redmond-based company has offered workarounds in its guidance to disable the MSDT URL protocol via a Windows Registry modification.
"If the calling application is a Microsoft Office application, by default, Microsoft Office opens documents from the internet in Protected View or Application Guard for Office, both of which prevent the current attack," Microsoft said.
This is not the first time Microsoft Office protocol schemes like "ms-msdt:" have come under the scanner for their potential misuse. Earlier this January, German cybersecurity company SySS disclosed how it's possible to open files directly via specially crafted URLs such as "ms-excel:ofv|u|https://192.168.1.10/poc[.]xls."