Zero-day Vulnerabilities in Microsoft Exchange Server [CVE-2022-41040 and CVE-2022-41082]

CVE numbers = CVE-2022-41040 and CVE-2022-41082

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

At this time, Microsoft is aware of limited targeted attacks using the two vulnerabilities to get into users’ systems.  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 of the two vulnerabilities.  

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

Mitigations

Microsoft Exchange Online Customers do not need to take any action. 

On premises Microsoft Exchange customers should review and apply the following URL Rewrite Instructions and block exposed Remote PowerShell ports. 

The current mitigation is to add a blocking rule in “IIS Manager -> Default Web Site -> Autodiscover -> URL Rewrite -> Actions” to block the known attack patterns. 

Microsoft has confirmed that the following URL Rewrite Instructions, which are currently being discussed publicly, are successful in breaking current attack chains. 

• Open the IIS Manager. 
• Expand the Default Web Site. 
• Select Autodiscover. 
• In the Feature View, click URL Rewrite. 
• In the Actions pane on the right-hand side, click Add Rules.  
• Select Request Blocking and click OK. 
• Add String “.*autodiscover\.json.*\@.*Powershell.*” (excluding quotes) and click OK.
• Expand the rule and select the rule with the Pattern “.*autodiscover\.json.*\@.*Powershell.*” and click Edit under Conditions. 
• Change the condition input from {URL} to {REQUEST_URI} 

Impact: There is no known impact to Exchange functionality if the URL Rewrite module is installed as recommended. 

Authenticated attackers who can access PowerShell Remoting on vulnerable Exchange systems will be able to trigger RCE using CVE-2022-41082. Blocking the ports used for Remote PowerShell can limit these attacks. 

• HTTP: 5985 
• HTTPS: 5986