# MA-866.092022: MyCERT Advisory - Microsoft Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server

**Date:** 30 Sep 2022  
**Source:** https://www.mycert.org.my/portal/advisory?id=MA-866.092022  
**Advisory ID:** MA-866.092022

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**1.0 Introduction**
Two zero-day vulnerabilities affecting Microsoft Exchange Server were reported recently this week. As of writing, Microsoft is already aware of the issue and is working on releasing a fix soon and providing temporary workarounds in the meantime.
The first vulnerability, identified as CVE-2022-41040, is a Server-Side Request Forgery (SSRF) vulnerability, while the second vulnerability is identified as CVE-2022-41082.
**2.0 Impact**
CVE-2022-41040 can enable an authenticated attacker to trigger CVE-2022-41082 remotely in these attacks and CVE-2022-41082 allows remote code execution (RCE) when PowerShell is accessible to the attacker. It should be noted that authenticated access to the vulnerable Exchange Server is necessary to exploit either of the two vulnerabilities successfully.
**3.0 Affected Products**
The affected Microsoft products are Microsoft Exchange Server 2013, 2016, and 2019.
**4.0 Recommendations**
Users and administrators of the affected Microsoft Exchange products are advised to follow and apply the mitigation steps based on the guide below while waiting for a patch to be released by Microsoft. 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. The steps are as below:
- 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 on 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
For more detailed information, kindly visit the URL below:
<https://msrc-blog.microsoft.com/2022/09/29/customer-guidance-for-reported-zero-day-vulnerabilities-in-microsoft-exchange-server/>
Generally, MyCERT advises users to be updated with the latest security announcements or release of patches by the vendor and follow best security practices to determine which updates should be applied.
For further enquiries, please contact MyCERT through the following channels:
E-mail: cyber999[at]cybersecurity.my 
Phone: 1-300-88-2999 (monitored during business hours) 
Mobile: +60 19 2665850 (24x7 call incident reporting) 
Business Hours: Mon - Fri 09:00 -18:00 MYT 
Web: <https://www.mycert.org.my> 
Twitter: <https://twitter.com/mycert> 
Facebook: <https://www.facebook.com/mycert.org.my>
**5.0    References·** <https://www.bleepingcomputer.com/news/security/new-microsoft-exchange-zero-day-actively-exploited-in-attacks/>
·       <https://www.gteltsc.vn/blog/warning-new-attack-campaign-utilized-a-new-0day-rce-vulnerability-on-microsoft-exchange-server-12715.html>
·       <https://doublepulsar.com/proxynotshell-the-story-of-the-claimed-zero-day-in-microsoft-exchange-5c63d963a9e9>
**·** <https://msrc-blog.microsoft.com/2022/09/29/customer-guidance-for-reported-zero-day-vulnerabilities-in-microsoft-exchange-server/>