December 2023 Windows Updates brought a patch for CVE-2023-36003, a privilege escalation vulnerability in Microsoft Windows XAML diagnostics API. The vulnerability allows a low-privileged Windows process to execute arbitrary code in a higher-privileged process running in the same user session, and is therefore useful for elevating from a non-admin to admin user.
Security researcher Michael Maltsev, who found this vulnerability and reported it to Microsoft in July 2023, wrote a detailed article and published a POC. These allowed us to reproduce the issue and create a micropatch for users of legacy Windows systems, which are no longer receiving security updates from Microsoft.
Our Micropatch
As Michael has already noted, there were two changes in the December version of Windows.UI.Xaml.dll, but only one seems to be related to this issue: namely the one that sets the security descriptor of the process’s XAML diagnostics API interface to the current process’s integrity level. Consequently, only processes that have at least the same integrity level as the target process will be allowed to utilize the affected functionality (and have arbitrary code executed in the target process).
Our micropatch is functionally identical to Microsoft’s.
Let’s see our
micropatch in action. A local unprivileged user launches the POC, which periodically attempts to locate a privileged process to sent the offensive XAML diagnostics request to. Another process (Windows Magnifier) is then launched as administrator; the POC quickly finds it and requests that it loads a malicious DLL that then spawns a new command window – as Administrator. This demonstrates that arbitrary code could be executed in the privileged process. With 0patch enabled, the POC fails to attack the privileged process as our patch makes sure that only high-integrity processes could send XAML diagnostics requests to the high-integrity process (Magnifier).
Note that in a real attack, the attacker would actually be malware silently running in the background, waiting for the user to launch another process with higher privileges and then attacking that process.
Micropatch Availability
Micropatches were written for the following security-adopted versions of Windows with all available Windows Updates installed:
- Windows 11 v21H1 – fully updated
- Windows 10 v21H1 – fully updated
- Windows 10 v20H2 – fully updated
- Windows 10 v2004 – fully updated
- Windows 10 v1909 – fully updated
- Windows 10 v1809 – fully updated
- Windows 10 v1803 – fully updated
Micropatches have already been distributed to, and applied on, all
online 0patch Agents in PRO or Enterprise accounts (unless Enterprise group settings prevent that).
Vulnerabilities like this one get discovered on a regular basis, and
attackers know about them all. 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 0patch.com, and email sales@0patch.com for a trial. Everything else will happen automatically. No computer reboot will be needed.
We would like to thank Michael Maltsev for sharing their analysis, which made it possible for us to create a
micropatch for this issue.
To learn more about 0patch, please visit our Help Center.
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