Microsoft Defender Will Soon Block Windows Password Theft
To prevent threat actors from abusing LSASS memory dumps, Microsoft has introduced security features that prevent access to the LSASS process. One of these security features is Credential Guard, which isolates the LSASS process in a virtualized container that prevents other processes from accessing it. However, this feature can lead to conflicts with drivers or applications, causing some organizations not to enable it. As a way to mitigate Windows credential theft without causing the conflicts introduced by Credential Guard, Microsoft will soon be enabling a Microsoft Defender Attack Surface Reduction (ASR) rule by default. The rule, ‘ Block credential stealing from the Windows local security authority subsystem,’ prevents processes from opening the LSASS process and dumping its memory, even if it has administrative privileges.
While enabling the ASR rule by default will significantly impact the stealing of Windows credentials, it is not a silver bullet by any means. This is because the full Attack Surface Reduction feature is only supported on Windows Enterprise licenses running Microsoft Defender as the primary antivirus. However, BleepingComputer’s tests show that the LSASS ASR rule also works on Windows 10 and Windows 11 Pro clients. Unfortunately, once another antivirus solution is installed, ASR is immediately disabled on the device. Furthermore, security researchers have discovered built-in Microsoft Defender exclusion paths allowing threat actors to run their tools from those filenames/directories to bypass the ASR rules and continue to dump the LSASS process. Mimikatz developer Benjamin Delpy told BleepingComputer that Microsoft probably added these built-in exclusions for another rule, but as exclusions affect ALL rules, it bypasses the LSASS restriction.
Read more of this story at Slashdot.