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Gustavo Palazolo and Ghanashyam Satpathy
Summary
On May 27, 2022, a Microsoft Office document was submitted from Belarus to VirusTotal, using a novel method to deliver its payload. This new technique was identified as a Zero-Day RCE (Remote Code Execution) vulnerability in Microsoft Support Diagnostic Tool (MSDT), which is now being tracked as CVE-2022-30190. As of this writing, it affects only Windows computers running with MSDT URI protocol enabled.
The methods of execution and net result of this vulnerability continue to expand as it gains more attention, similar to what we observed with Log4j. CVE-2022-30190 is also being called Follina, because the sample uploaded to VirusTotal references 0438, which is the area code for Follina in Italy.
This vulnerability does not require any macros, which are now disabled by default on files downloaded from the internet. The exploit can be achieved through crafted URLs that use the ms-msdt URL protocol, which will eventually load and execute code. The attack surface for MSDT Protocol in Office is also quite large. Furthermore, the document spotted on May 27 is using Living-off-the-Land techniques by abusing “msdt.exe” and “certutil.exe” binaries. At this point, there are a few public PoCs created by security researchers available on GitHub.
Microsoft has released a few workarounds users can implement to be protected against this vulnerability. The official fix has not yet been released.
CVE-2022-30190
In this analysis, we created a non-weaponized sample using one of the public PoCs available on GitHub, to demonstrate how it works.
Like CVE-2021-40444, the document may trigger the vulnerability by abusing the OOXML relationships to automatically download the content from an external URL. In this case, the URL is pointing to localhost as we are using the PoC code.
