Monday, June 5, 2023

Micropatches Released For Remote Code Execution in Windows OLE (CVE-2023-29325)



May 2023 Windows Updates brought a fix for CVE-2023-29325, a remote code execution vulnerability in Microsoft OLE (Object Linking and Embedding). The vulnerability was reported to Microsoft by Will Dormann with Vul Labs.

Will found that two of the many COM objects installed on every Windows system by default merely have to be referenced by their respective CLSIDs in a rich text email for Outlook to experience an access violation exception.

There is almost no public information on what these two COM objects were intended to do on a Windows system, but since Microsoft's fix was to block them, they probably aren't essential to any important operation. While Microsoft appears to have blocked these offensive/vulnerable COM objects via COM activation filter, they provided no remedy for unsupported Windows versions such as Windows 7 or older Windows 10. Furthermore, still-supported Office versions were also patched to prevent usage of these two COM objects, but older versions like 2010 or 2013 weren't.

For our users of older Office versions on older Windows systems we therefore had to create a patch of our own.

Our patch does effectively the same as Microsoft's does on still-supported Office versions: if a COM object is referenced with one of the "offending" CLSIDs, object activation is prevented and instead of instantiating such object, Office just writes out the CLSID and the associated DLL name.

Let's see our micropatch in action. With 0patch disabled, opening a POC email immediately crashes Outlook. With 0patch enabled, Outlook displays an email with CLSID printed out in the body, but doesn't crash.

Micropatch Availability

Our micropatch was written for the following security-adopted versions of Office with all available updates installed:

  1. Office 2010
  2. Office 2013 
This micropatch has already been distributed to, and applied on, all online 0patch Agents in PRO or Enterprise accounts (unless Enterprise group settings prevent that). No restart was needed, and Office got patched without relaunching even if it was running at the time.

Vulnerabilities like this one get discovered on a regular basis, and attackers know about them. If you're using Windows that aren't receiving official security updates anymore, 0patch will make sure these vulnerabilities won't be exploited on your computers - and you won't even have to know or care about these things.

If you're new to 0patch, create a free account in 0patch Central, then install and register 0patch Agent from, and email for a trial. Everything else will happen automatically. No computer reboot will be needed.

To learn more about 0patch, please visit our Help Center

We'd like to thank Will Dormann for sharing vulnerability details, which allowed us to create a micropatch and protect our users against this attack. We also encourage all security researchers to privately share their analyses with us for micropatching.


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