Customer Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server

September 30, 2022 updates:

  • Added link to Microsoft Security blog in Summary.
  • Microsoft created a script for the URL Rewrite mitigation steps and modified step 6 in the Mitigations section.
  • Microsoft released the Exchange Server Emergency Mitigation Service (EMS) mitigation for this issue. More information is in the Mitigations section. 
  • Antimalware Scan Interface (AMSI) guidance, and auditing AV exclusions to optimize detection, and blocking of the Exchange vulnerability exploitation in the Detections section.
  • Microsoft Sentinel hunting queries in the Detections section.


Microsoft is investigating two reported zero-day vulnerabilities affecting Microsoft Exchange Server 2013, Exchange Server 2016, and Exchange Server 2019. The first one, identified as CVE-2022-41040, is a Server-Side Request Forgery (SSRF) vulnerability, and the second one, identified as CVE-2022-41082, allows Remote Code Execution (RCE) when PowerShell is accessible to the attacker.  

Currently, Microsoft is aware of limited targeted attacks using these two vulnerabilities.  In these attacks, CVE-2022-41040 can enable an authenticated attacker to remotely trigger CVE-2022-41082. It should be noted that authenticated access to the vulnerable Exchange Server is necessary to successfully exploit either vulnerability.

We are working on an accelerated timeline to release a fix. Until then, we’re providing mitigations and the detections guidance below to help customers protect themselves from these attacks. 

Microsoft Exchange Online has detections and mitigations to protect customers. As always, Microsoft is monitoring these detections for malicious activity and we’ll respond accordingly if necessary to protect customers.

Microsoft Security Threat Intelligence teams have provided further analysis of observed activity along with mitigation and detection guidance in a new Microsoft Security blog.

We will also continue to provide updates here to help keep customers informed. 


Exchange Online customers do not need to take any action.

The current Exchange Server mitigation is to add a blocking rule in “IIS Manager -> Default Web Site -> URL Rewrite -> Actions” to block the known attack patterns. Exchange Server customers should review and choose only one of the following three mitigation options.

Option 1: For customers who have the Exchange Server Emergency Mitigation Service (EMS) enabled, Microsoft released the URL Rewrite mitigation for Exchange Server 2016 and Exchange Server 2019. The mitigation will be enabled automatically. Please see this blog post for more information on this service and how to check active mitigations.

Option 2: Microsoft created the following script for the URL Rewrite mitigation steps. 

Option 3: Customers can follow the below instructions, which are currently being discussed publicly and are successful in breaking current attack chains. 1. Open IIS Manager. 
2. Select Default Web Site.
3. In the Feature View, click URL Rewrite.

4. In the Actions pane on the right-hand side, click Add Rule(s)…  

5. Select Request Blocking and click OK. 

6. Add the string “.*autodiscover\.json.*\@.*Powershell.*” (excluding quotes).
7. Select Regular Expression under Using.
8. Select Abort Request under How to block and then click OK.

9. Expand the rule and select the rule with the pattern .*autodiscover\.json.*\@.*Powershell.* and click Edit under Conditions

10. Change the Condition input from {URL} to {REQUEST_URI}

NOTE: If you need to change any rule it is best to delete and recreate it.

Impact: There is no known effect on Exchange functionality if URL Rewrite is installed as recommended. 


Microsoft Sentinel 

Based on what we’re seeing in the wild, looking for the techniques listed below will help defenders. Our post on Web Shell Threat Hunting with Microsoft Sentinel also provides guidance on looking for web shells in general.  

The Exchange SSRF Autodiscover ProxyShell detection, which was created in response to ProxyShell, can be used for queries as there are similarities in function with this threat. Also, the new Exchange Server Suspicious File Downloads and Exchange Worker Process Making Remote Call queries specifically look for suspicious downloads or activity in IIS logs. In addition to those, we have a few more that might be helpful when looking for post-exploitation activity:

Microsoft Defender for Endpoint 
Microsoft Defender for Endpoint detects post-exploitation activity. The following alerts can be related to this threat:  

  • Possible web shell installation 
  • Possible IIS web shell
  • Suspicious Exchange Process Execution 
  • Possible exploitation of Exchange Server vulnerabilities 
  • Suspicious processes indicative of a web shell 
  • Possible IIS compromise 

Customers with Microsoft Defender Antivirus enabled can also detect the web shell malware used in exploitation of this vulnerability in-the-wild as of this writing with the following alerts:

  • ‘Chopper’ malware was detected on an IIS Web server 
  • ‘Chopper’ high-severity malware was detected 

Microsoft Defender Antivirus 
Microsoft Exchange AMSI integration and Antivirus Exclusions

Exchange supports the integration with the Antimalware Scan Interface (AMSI) since the June 2021 Quarterly Updates for Exchange. It is highly recommended to ensure these updates are installed and AMSI is working using the guidance provided by the Exchange Team, as this integration provides the best ability for Defender Antivirus to detect and block exploitation of vulnerabilities on Exchange.

Many organizations exclude Exchange directories from antivirus scans for performance reasons. It’s highly recommended to audit AV exclusions on the Exchange systems and assess if they can be removed without impacting performance and still ensure the highest level of protection. Exclusions can be managed via Group Policy, PowerShell, or systems management tools like System Center Configuration Manager.

To audit AV exclusions on an Exchange Server running Defender Antivirus, launch the Get-MpPreference command from an elevated PowerShell prompt.

If exclusions cannot be removed for Exchange processes and folders, running Quick Scan in Defender Antivirus scans Exchange directories and files regardless of exclusions.

Microsoft Defender Antivirus (EPP) provides detections and protections for components and behaviors related to this threat under the following signatures: