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<blockquote data-quote="Deleted member 65228" data-source="post: 734683"><p>[USER=37647]@shmu26[/USER] As far as I am aware, there are only 12 Attack Surface Reduction (ASR) rules.</p><p></p><p>[SPOILER]</p><p>I have only started investigating it properly (I verified that the prevention of RCE for that rule does indeed work against NtAllocateVirtualMemory, I am yet to test NtWriteVirtualMemory and others).</p><p></p><p>I attached a debugger to the correct process responsible for carrying out the virtual memory operation on the target process (which should have been blocked) and set a break-point for NtAllocateVirtualMemory, then I saw the call go through and got a hit for NtAllocateVirtualMemory (NTOSKRNL) from kernel debugging. However, Attack Surface Reduction (ASR) kept its word and blocked that virtual memory operation like it was supposed to. As in, the operation was not successful. If I recall correctly, it returned an NTSTATUS code of STATUS_ACCESS_DENIED while the RCE rule was enabled only. NtAllocateVirtualMemory (NTOSKRNL) calls MiAllocateVirtualMemory (NTOSKRNL) anyway so it is likely a lot more deeper embedded.</p><p></p><p>The actual RCE IMO would be getting the memory changed (e.g. NtWriteVirtualMemory), which is why this is only partly tested. Virtual memory operations for remote memory allocation is actually an optional thing with RCE, but I wanted to start with it when I had time the other day. NtProtectVirtualMemory, NtUnmapViewOfSection and for curiosity... Reading via NtReadVirtualMemory is also on my list. </p><p></p><p>Therefore, at-least now we know that the rule for "Block Office applications from injecting code into other processes" has been partly tested, for now for remote virtual memory allocation. I'll do more testing with it when I have more time, hopefully soon.</p><p></p><p>[ This is related to 75668C1F-73B5-4CF0-BB93-3ECF5CB7CC84 ]</p><p>[/SPOILER]</p><p></p><p><strong>Anyway, based on your registry, it seems you have:</strong></p><p>1. "Block Office applications from creating executable content" (3B576869-A4EC-4529-8536-B80A7769E899)</p><p>2. "Block execution of potentially obfuscated scripts" (5BEB7EFE-FD9A-4556-801D-275E5FFC04CC)</p><p>3. "Block Office applications from injecting code into other processes" (75668C1F-73B5-4CF0-BB93-3ECF5CB7CC84)</p><p>4. "Block Win32 API calls from Office macro" (92E97FA1-2EDF-4476-BDD6-9DD0B4DDDC7B)</p><p>5. "Block credential stealing from the Windows local security authority subsystem (lsass.exe)" (9e6c4e1f-7d60-472f-ba1a-a39ef669e4b2)</p><p>6. "Block executable content from email client and webmail" (BE9BA2D9-53EA-4CDC-84E5-9B1EEEE46550)</p><p>7. "Block JavaScript or VBScript from launching downloaded executable content" (D3E037E1-3EB8-44C8-A917-57927947596D)</p><p>8. "Block Office applications from creating child processes" (D4F940AB-401B-4EFC-AADC-AD5F3C50688A)</p><p></p><p><strong>The ones you do not seem to have enabled:</strong></p><p>1. "Block executable files from running unless they meet a prevalence, age, or trusted list criteria" (01443614-cd74-433a-b99e-2ecdc07bfc25)</p><p>2. "Use advanced protection against ransomware" (c1db55ab-c21a-4637-bb3f-a12568109d35)</p><p>3. "Block process creations originating from PSExec and WMI commands" (d1e49aac-8f56-4280-b9ba-993a6d77406c)</p><p>4. "Block untrusted and unsigned processes that run from USB" (b2b3f03d-6a65-4f7b-a9c7-1c7ef74a9ba4)</p><p></p><p>Therefore, yes, it appears you do have the entry for credential theft with lsass.exe. However, the rule you were specifically interested in and posted a screenshot of is for child process creation prevention.</p><p></p><p>Source:</p><p><a href="https://docs.microsoft.com/en-us/windows/security/threat-protection/windows-defender-exploit-guard/attack-surface-reduction-exploit-guard" target="_blank">Use Attack surface reduction rules to prevent malware infection</a></p></blockquote><p></p>
[QUOTE="Deleted member 65228, post: 734683"] [USER=37647]@shmu26[/USER] As far as I am aware, there are only 12 Attack Surface Reduction (ASR) rules. [SPOILER] I have only started investigating it properly (I verified that the prevention of RCE for that rule does indeed work against NtAllocateVirtualMemory, I am yet to test NtWriteVirtualMemory and others). I attached a debugger to the correct process responsible for carrying out the virtual memory operation on the target process (which should have been blocked) and set a break-point for NtAllocateVirtualMemory, then I saw the call go through and got a hit for NtAllocateVirtualMemory (NTOSKRNL) from kernel debugging. However, Attack Surface Reduction (ASR) kept its word and blocked that virtual memory operation like it was supposed to. As in, the operation was not successful. If I recall correctly, it returned an NTSTATUS code of STATUS_ACCESS_DENIED while the RCE rule was enabled only. NtAllocateVirtualMemory (NTOSKRNL) calls MiAllocateVirtualMemory (NTOSKRNL) anyway so it is likely a lot more deeper embedded. The actual RCE IMO would be getting the memory changed (e.g. NtWriteVirtualMemory), which is why this is only partly tested. Virtual memory operations for remote memory allocation is actually an optional thing with RCE, but I wanted to start with it when I had time the other day. NtProtectVirtualMemory, NtUnmapViewOfSection and for curiosity... Reading via NtReadVirtualMemory is also on my list. Therefore, at-least now we know that the rule for "Block Office applications from injecting code into other processes" has been partly tested, for now for remote virtual memory allocation. I'll do more testing with it when I have more time, hopefully soon. [ This is related to 75668C1F-73B5-4CF0-BB93-3ECF5CB7CC84 ] [/SPOILER] [B]Anyway, based on your registry, it seems you have:[/B] 1. "Block Office applications from creating executable content" (3B576869-A4EC-4529-8536-B80A7769E899) 2. "Block execution of potentially obfuscated scripts" (5BEB7EFE-FD9A-4556-801D-275E5FFC04CC) 3. "Block Office applications from injecting code into other processes" (75668C1F-73B5-4CF0-BB93-3ECF5CB7CC84) 4. "Block Win32 API calls from Office macro" (92E97FA1-2EDF-4476-BDD6-9DD0B4DDDC7B) 5. "Block credential stealing from the Windows local security authority subsystem (lsass.exe)" (9e6c4e1f-7d60-472f-ba1a-a39ef669e4b2) 6. "Block executable content from email client and webmail" (BE9BA2D9-53EA-4CDC-84E5-9B1EEEE46550) 7. "Block JavaScript or VBScript from launching downloaded executable content" (D3E037E1-3EB8-44C8-A917-57927947596D) 8. "Block Office applications from creating child processes" (D4F940AB-401B-4EFC-AADC-AD5F3C50688A) [B]The ones you do not seem to have enabled:[/B] 1. "Block executable files from running unless they meet a prevalence, age, or trusted list criteria" (01443614-cd74-433a-b99e-2ecdc07bfc25) 2. "Use advanced protection against ransomware" (c1db55ab-c21a-4637-bb3f-a12568109d35) 3. "Block process creations originating from PSExec and WMI commands" (d1e49aac-8f56-4280-b9ba-993a6d77406c) 4. "Block untrusted and unsigned processes that run from USB" (b2b3f03d-6a65-4f7b-a9c7-1c7ef74a9ba4) Therefore, yes, it appears you do have the entry for credential theft with lsass.exe. However, the rule you were specifically interested in and posted a screenshot of is for child process creation prevention. Source: [URL='https://docs.microsoft.com/en-us/windows/security/threat-protection/windows-defender-exploit-guard/attack-surface-reduction-exploit-guard']Use Attack surface reduction rules to prevent malware infection[/URL] [/QUOTE]
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