Attack surface reduction rules reference - Microsoft Defender for Endpoint (2024)

Applies to:

• Microsoft Microsoft Defender XDR for Endpoint Plan 1
• Microsoft Defender for Endpoint Plan 2
• Microsoft Defender XDR
• Microsoft Defender Antivirus

Platforms:

• Windows

This article provides information about Microsoft Defender for Endpoint attack surface reduction rules (ASR rules):

• ASR rules supported operating system versions
• ASR rules supported configuration management systems
• Per ASR rule alert and notification details
• ASR rule to GUID matrix
• ASR rule modes
• Per-rule-descriptions

Attack surface reduction rules by type

Attack surface reduction rules are categorized as one of two types:

• Standard protection rules: Are the minimum set of rules which Microsoft recommends you always enable, while you're evaluating the effect and configuration needs of the other ASR rules. These rules typically have minimal-to-no noticeable impact on the end user.

• Other rules: Rules that require some measure of following the documented deployment steps [Plan > Test (audit) > Enable (block/warn modes)], as documented in the Attack surface reduction rules deployment guide

For the easiest method to enable the standard protection rules, see: Simplified standard protection option.

Microsoft Defender Antivirus exclusions and ASR rules

Microsoft Defender Antivirus exclusions apply to some Microsoft Defender for Endpoint capabilities, such as some of the attack surface reduction rules.

The following ASR rules DO NOT honor Microsoft Defender Antivirus exclusions:

ASR rules and Defender for Endpoint Indicators of Compromise (IOC)

The following ASR rules DO NOT honor Microsoft Defender for Endpoint Indicators of Compromise (IOC):

ASR rules supported operating systems

The following table lists the supported operating systems for rules that are currently released to general availability. The rules are listed alphabetical order in this table.

(1) Refers to the modern unified solution for Windows Server 2012 and 2016. For more information, see Onboard Windows Servers to the Defender for Endpoint service.

(2) For WindowsServer 2016 and WindowsServer 2012R2, the minimum required version of Microsoft Endpoint Configuration Manager is version 2111.

(3) Version and build number apply only to Windows10.

ASR rules supported configuration management systems

Links to information about configuration management system versions referenced in this table are listed below this table.

(1) You can configure attack surface reduction rules on a per-rule basis by using any rule's GUID.

• Configuration Manager CB 1710
• Configuration Manager CB 1802
• Microsoft Configuration Manager CB 1710
• System Center Configuration Manager (SCCM) CB 1710
  SCCM is now Microsoft Configuration Manager.

Per ASR rule alert and notification details

Toast notifications are generated for all rules in Block mode. Rules in any other mode don't generate toast notifications.

For rules with the "Rule State" specified:

• ASR rules with <ASR Rule, Rule State> combinations are used to surface alerts (toast notifications) on Microsoft Defender for Endpoint only for devices at cloud block level High. Devices not at High cloud block level won't generate alerts for any <ASR Rule, Rule State> combinations
• EDR alerts are generated for ASR rules in the specified states, for devices at cloud block level High+

ASR rule to GUID matrix

ASR rule modes

• Not configured or Disable: The state in which the ASR rule isn't enabled or is disabled. The code for this state = 0.
• Block: The state in which the ASR rule is enabled. The code for this state is 1.
• Audit: The state in which the ASR rule is evaluated for the effect it would have on the organization or environment if enabled (set to block or warn). The code for this state is 2.
• Warn The state in which the ASR rule is enabled and presents a notification to the end-user, but permits the end-user to bypass the block. The code for this state is 6.

Warn mode is a block-mode type that alerts users about potentially risky actions. Users can choose to bypass the block warning message and allow the underlying action. Users can select OK to enforce the block, or select the bypass option - Unblock - through the end-user pop-up toast notification that is generated at the time of the block. After the warning is unblocked, the operation is allowed until the next time the warning message occurs, at which time the end-user will need to reperform the action.

When the allow button is clicked, the block is suppressed for 24 hours. After 24 hours, the end-user will need to allow the block again. The warn mode for ASR rules is only supported for RS5+ (1809+) devices. If bypass is assigned to ASR rules on devices with older versions, the rule will be in blocked mode.

You can also set a rule in warn mode via PowerShell by specifying the AttackSurfaceReductionRules_Actions as "Warn". For example:

Add-MpPreference -AttackSurfaceReductionRules_Ids 56a863a9-875e-4185-98a7-b882c64b5ce5 -AttackSurfaceReductionRules_Actions Warn

Per rule descriptions

Block abuse of exploited vulnerable signed drivers

This rule prevents an application from writing a vulnerable signed driver to disk. In-the-wild, vulnerable signed drivers can be exploited by local applications - that have sufficient privileges - to gain access to the kernel. Vulnerable signed drivers enable attackers to disable or circumvent security solutions, eventually leading to system compromise.

The Block abuse of exploited vulnerable signed drivers rule doesn't block a driver already existing on the system from being loaded.

Intune Name: Block abuse of exploited vulnerable signed drivers

Configuration Manager name: Not yet available

GUID: 56a863a9-875e-4185-98a7-b882c64b5ce5

Advanced hunting action type:

• AsrVulnerableSignedDriverAudited
• AsrVulnerableSignedDriverBlocked

Block Adobe Reader from creating child processes

This rule prevents attacks by blocking Adobe Reader from creating processes.

Malware can download and launch payloads and break out of Adobe Reader through social engineering or exploits. By blocking child processes from being generated by Adobe Reader, malware attempting to use Adobe Reader as an attack vector are prevented from spreading.

Intune name: Process creation from Adobe Reader (beta)

Configuration Manager name: Not yet available

GUID: 7674ba52-37eb-4a4f-a9a1-f0f9a1619a2c

Advanced hunting action type:

• AsrAdobeReaderChildProcessAudited
• AsrAdobeReaderChildProcessBlocked

Dependencies: Microsoft Defender Antivirus

Block all Office applications from creating child processes

This rule blocks Office apps from creating child processes. Office apps include Word, Excel, PowerPoint, OneNote, and Access.

Creating malicious child processes is a common malware strategy. Malware that abuses Office as a vector often runs VBA macros and exploit code to download and attempt to run more payloads. However, some legitimate line-of-business applications might also generate child processes for benign purposes; such as spawning a command prompt or using PowerShell to configure registry settings.

Intune name: Office apps launching child processes

Configuration Manager name: Block Office application from creating child processes

GUID: d4f940ab-401b-4efc-aadc-ad5f3c50688a

Advanced hunting action type:

• AsrOfficeChildProcessAudited
• AsrOfficeChildProcessBlocked

Dependencies: Microsoft Defender Antivirus

Block credential stealing from the Windows local security authority subsystem

This rule helps prevent credential stealing by locking down Local Security Authority Subsystem Service (LSASS).

LSASS authenticates users who sign in on a Windows computer. Microsoft Defender Credential Guard in Windows normally prevents attempts to extract credentials from LSASS. Some organizations can't enable Credential Guard on all of their computers because of compatibility issues with custom smartcard drivers or other programs that load into the Local Security Authority (LSA). In these cases, attackers can use tools like Mimikatz to scrape cleartext passwords and NTLM hashes from LSASS.

By default the state of this rule is set to block. In most cases, many processes make calls to LSASS for access rights that are not needed. For example, such as when the initial block from the ASR rule results in a subsequent call for a lesser privilege which subsequently succeeds. For information about the types of rights that are typically requested in process calls to LSASS, see: Process Security and Access Rights.

Enabling this rule doesn't provide additional protection if you have LSA protection enabled since the ASR rule and LSA protection work similarly. However, when LSA protection cannot be enabled, this rule can be configured to provide equivalent protection against malware that target lsass.exe.

Intune name: Flag credential stealing from the Windows local security authority subsystem

Configuration Manager name: Block credential stealing from the Windows local security authority subsystem

GUID: 9e6c4e1f-7d60-472f-ba1a-a39ef669e4b2

Advanced hunting action type:

• AsrLsassCredentialTheftAudited
• AsrLsassCredentialTheftBlocked

Dependencies: Microsoft Defender Antivirus

Block executable content from email client and webmail

This rule blocks email opened within the Microsoft Outlook application, or Outlook.com and other popular webmail providers from propagating the following file types:

• Executable files (such as .exe, .dll, or .scr)
• Script files (such as a PowerShell .ps1, Visual Basic .vbs, or JavaScript .js file)

Intune name: Execution of executable content (exe, dll, ps, js, vbs, etc.) dropped from email (webmail/mail client) (no exceptions)

Microsoft Configuration Manager name: Block executable content from email client and webmail

GUID: be9ba2d9-53ea-4cdc-84e5-9b1eeee46550

Advanced hunting action type:

• AsrExecutableEmailContentAudited
• AsrExecutableEmailContentBlocked

Dependencies: Microsoft Defender Antivirus

Block executable files from running unless they meet a prevalence, age, or trusted list criterion

This rule blocks executable files, such as .exe, .dll, or .scr, from launching. Thus, launching untrusted or unknown executable files can be risky, as it might not be initially clear if the files are malicious.

Intune name: Executables that don't meet a prevalence, age, or trusted list criteria

Configuration Manager name: Block executable files from running unless they meet a prevalence, age, or trusted list criteria

GUID: 01443614-cd74-433a-b99e-2ecdc07bfc25

Advanced hunting action type:

• AsrUntrustedExecutableAudited
• AsrUntrustedExecutableBlocked

Dependencies: Microsoft Defender Antivirus, Cloud Protection

Block execution of potentially obfuscated scripts

This rule detects suspicious properties within an obfuscated script.

Script obfuscation is a common technique that both malware authors and legitimate applications use to hide intellectual property or decrease script loading times. Malware authors also use obfuscation to make malicious code harder to read, which hampers close scrutiny by humans and security software.

Intune name: Obfuscated js/vbs/ps/macro code

Configuration Manager name: Block execution of potentially obfuscated scripts

GUID: 5beb7efe-fd9a-4556-801d-275e5ffc04cc

Advanced hunting action type:

• AsrObfuscatedScriptAudited
• AsrObfuscatedScriptBlocked

Dependencies: Microsoft Defender Antivirus, AntiMalware Scan Interface (AMSI)

Block JavaScript or VBScript from launching downloaded executable content

This rule prevents scripts from launching potentially malicious downloaded content. Malware written in JavaScript or VBScript often acts as a downloader to fetch and launch other malware from the Internet.

Although not common, line-of-business applications sometimes use scripts to download and launch installers.

Intune name: js/vbs executing payload downloaded from Internet (no exceptions)

Configuration Manager name: Block JavaScript or VBScript from launching downloaded executable content

GUID: d3e037e1-3eb8-44c8-a917-57927947596d

Advanced hunting action type:

• AsrScriptExecutableDownloadAudited
• AsrScriptExecutableDownloadBlocked

Dependencies: Microsoft Defender Antivirus, AMSI

Block Office applications from creating executable content

This rule prevents Office apps, including Word, Excel, and PowerPoint, from creating potentially malicious executable content, by blocking malicious code from being written to disk.

Malware that abuses Office as a vector might attempt to break out of Office and save malicious components to disk. These malicious components would survive a computer reboot and persist on the system. Therefore, this rule defends against a common persistence technique. This rule also blocks execution of untrusted files that may have been saved by Office macros that are allowed to run in Office files.

Intune name: Office apps/macros creating executable content

Configuration Manager name: Block Office applications from creating executable content

GUID: 3b576869-a4ec-4529-8536-b80a7769e899

Advanced hunting action type:

• AsrExecutableOfficeContentAudited
• AsrExecutableOfficeContentBlocked

Dependencies: Microsoft Defender Antivirus, RPC

Block Office applications from injecting code into other processes

This rule blocks code injection attempts from Office apps into other processes.

Attackers might attempt to use Office apps to migrate malicious code into other processes through code injection, so the code can masquerade as a clean process.

There are no known legitimate business purposes for using code injection.

This rule applies to Word, Excel, OneNote, and PowerPoint.

Intune name: Office apps injecting code into other processes (no exceptions)

Configuration Manager name: Block Office applications from injecting code into other processes

GUID: 75668c1f-73b5-4cf0-bb93-3ecf5cb7cc84

Advanced hunting action type:

• AsrOfficeProcessInjectionAudited
• AsrOfficeProcessInjectionBlocked

Dependencies: Microsoft Defender Antivirus

Block Office communication application from creating child processes

This rule prevents Outlook from creating child processes, while still allowing legitimate Outlook functions.

This rule protects against social engineering attacks and prevents exploiting code from abusing vulnerabilities in Outlook. It also protects against Outlook rules and forms exploits that attackers can use when a user's credentials are compromised.

Intune name: Process creation from Office communication products (beta)

Configuration Manager name: Not available

GUID: 26190899-1602-49e8-8b27-eb1d0a1ce869

Advanced hunting action type:

• AsrOfficeCommAppChildProcessAudited
• AsrOfficeCommAppChildProcessBlocked

Dependencies: Microsoft Defender Antivirus

Block persistence through WMI event subscription

This rule prevents malware from abusing WMI to attain persistence on a device.

Fileless threats employ various tactics to stay hidden, to avoid being seen in the file system, and to gain periodic execution control. Some threats can abuse the WMI repository and event model to stay hidden.

Intune name: Persistence through WMI event subscription

Configuration Manager name: Not available

GUID: e6db77e5-3df2-4cf1-b95a-636979351e5b

Advanced hunting action type:

• AsrPersistenceThroughWmiAudited
• AsrPersistenceThroughWmiBlocked

Dependencies: Microsoft Defender Antivirus, RPC

Block process creations originating from PSExec and WMI commands

This rule blocks processes created through PsExec and WMI from running. Both PsExec and WMI can remotely execute code. There's a risk of malware abusing functionality of PsExec and WMI for command and control purposes, or to spread an infection throughout an organization's network.

Intune name: Process creation from PSExec and WMI commands

Configuration Manager name: Not applicable

GUID: d1e49aac-8f56-4280-b9ba-993a6d77406c

Advanced hunting action type:

• AsrPsexecWmiChildProcessAudited
• AsrPsexecWmiChildProcessBlocked

Dependencies: Microsoft Defender Antivirus

Block rebooting machine in Safe Mode (preview)

This rule prevents the execution of commands to restart machines in Safe Mode.

Safe Mode is a diagnostic mode that only loads the essential files and drivers needed for Windows to run. However, in Safe Mode, many security products are either disabled or operate in a limited capacity, which allows attackers to further launch tampering commands, or simply execute and encrypt all files on the machine. This rule blocks such attacks by preventing processes from restarting machines in Safe Mode.

Intune Name: [PREVIEW] Block rebooting machine in Safe Mode

Configuration Manager name: Not yet available

GUID: 33ddedf1-c6e0-47cb-833e-de6133960387

Dependencies: Microsoft Defender Antivirus

Block untrusted and unsigned processes that run from USB

With this rule, admins can prevent unsigned or untrusted executable files from running from USB removable drives, including SD cards. Blocked file types include executable files (such as .exe, .dll, or .scr)

Intune name: Untrusted and unsigned processes that run from USB

Configuration Manager name: Block untrusted and unsigned processes that run from USB

GUID: b2b3f03d-6a65-4f7b-a9c7-1c7ef74a9ba4

Advanced hunting action type:

• AsrUntrustedUsbProcessAudited
• AsrUntrustedUsbProcessBlocked

Dependencies: Microsoft Defender Antivirus

Block use of copied or impersonated system tools (preview)

This rule blocks the use of executable files that are identified as copies of Windows system tools. These files are either duplicates or impostors of the original system tools.

Some malicious programs may try to copy or impersonate Windows system tools to avoid detection or gain privileges. Allowing such executable files can lead to potential attacks. This rule prevents propagation and execution of such duplicates and impostors of the system tools on Windows machines.

Intune Name: [PREVIEW] Block use of copied or impersonated system tools

Configuration Manager name: Not yet available

GUID: c0033c00-d16d-4114-a5a0-dc9b3a7d2ceb

Dependencies: Microsoft Defender Antivirus

Block Webshell creation for Servers

This rule blocks web shell script creation on Microsoft Server, Exchange Role.

A web shell script is a specifically crafted script that allows an attacker to control the compromised server. A web shell may include functionalities such as receiving and executing malicious commands, downloading and executing malicious files, stealing and exfiltrating credentials and sensitive information, identifying potential targets etc.

Intune name: Block Webshell creation for Servers

GUID: a8f5898e-1dc8-49a9-9878-85004b8a61e6

Dependencies: Microsoft Defender Antivirus

Block Win32 API calls from Office macros

This rule prevents VBA macros from calling Win32 APIs.

Office VBA enables Win32 API calls. Malware can abuse this capability, such as calling Win32 APIs to launch malicious shellcode without writing anything directly to disk. Most organizations don't rely on the ability to call Win32 APIs in their day-to-day functioning, even if they use macros in other ways.

Intune name: Win32 imports from Office macro code

Configuration Manager name: Block Win32 API calls from Office macros

GUID: 92e97fa1-2edf-4476-bdd6-9dd0b4dddc7b

Advanced hunting action type:

• AsrOfficeMacroWin32ApiCallsAudited
• AsrOfficeMacroWin32ApiCallsBlocked

Dependencies: Microsoft Defender Antivirus, AMSI

Use advanced protection against ransomware

This rule provides an extra layer of protection against ransomware. It uses both client and cloud heuristics to determine whether a file resembles ransomware. This rule doesn't block files that have one or more of the following characteristics:

• The file has already been found to be unharmful in the Microsoft cloud.
• The file is a valid signed file.
• The file is prevalent enough to not be considered as ransomware.

The rule tends to err on the side of caution to prevent ransomware.

Intune name: Advanced ransomware protection

Configuration Manager name: Use advanced protection against ransomware

GUID: c1db55ab-c21a-4637-bb3f-a12568109d35

Advanced hunting action type:

• AsrRansomwareAudited
• AsrRansomwareBlocked

Dependencies: Microsoft Defender Antivirus, Cloud Protection

See also

• Attack surface reduction rules deployment overview
• Plan attack surface reduction rules deployment
• Test attack surface reduction rules
• Enable attack surface reduction rules
• Operationalize attack surface reduction rules
• Attack surface reduction rules report
• Attack surface reduction rules reference
• Exclusions for Microsoft Defender for Endpoint and Microsoft Defender Antivirus