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Vulnerabilities

Exploitation of Microsoft Exchange Servers seen in the wild

LATEST UPDATE (04/10/2022)

The latest guidance from Microsoft (released on the 02/10/2022) says to disable administrators from being able to execute remote PowerShell via the exchange PowerShell web endpoint /PowerShell

Exchange Web Services in IIS

Customer Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server – Microsoft Security Response Center

Read more: Exploitation of Microsoft Exchange Servers seen in the wild

October 2, 2022 updates:

  • Added to the Mitigations section: we strongly recommend Exchange Server customers to disable remote PowerShell access for non-admin users in your organization. Guidance on how to do this for single user or multiple users is here.  
  • Updated Detection section to refer to Analyzing attacks using the Exchange vulnerabilities CVE-2022-41040 and CVE-2022-41082.

Additional mitigations

  • Remove exchange web services from the internet (there are reasons to do and not do this)
  • Restrict hybrid servers to allow OWA to O365 only
  • Leverage dynamic blocking
  • Greynoise has a list of IPs known here: https://api.greynoise.io/v3/tags/8bf9b766-bf0f-452f-80bf-1d0903847793/ips?format=txt&token=rYZCpLOTf6UnUbBoUpF3Q

Obviously bear in mind this needs auth! but also auth isn’t always that hard..

Microsoft Research have just released (0825 30/09/2022) this: Customer Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server – Microsoft Security Response Center

Microsoft have released a Exchange Server Emergency Mitigation (EMS) which includes URL re-write rules to HELP mitigate this (but likely don’t eliminate all risks due to potential bypasses)

New security feature in September 2021 Cumulative Update for Exchange Server – Microsoft Tech Community

Current Scenario (Updated 11:27 30/09/2022)

Likely “Zero day” exploit in the wild being used to attack exchange servers via a simmilar endpoint to ProxyShell. A mitigation is to apply URL rewrite rules, or to disconect the service internet from untrsuted networks until a patch is available. The Exploit is reported to required AUTHENTICATION, which may significantly limit the volume of exploitation (however credentials are only a phish away). It’s also reported the exploitation in the wild used /Powershell after exploiting the autodiscover endpoint.

Overview (orginal post area)

Yesterday it was reported there was a “new” zero day vulnerability being exploited in the wild. But there appears to be some confusion and a lack of speciifc evidence to showcase the vulnerability being “new” or simply being a differnt exploit path/approach for an existing CVE (e.g. ProxyShell).

The situation from my pov (at time of writing) is still unclear. It would be odd to not advise people ensure they are running the latest supported Exchange CU and Security update release (check both!) – if the exploits are 0-day (which it looks like they are) you will need to also patch when MS release a patch!

  • You may also wish to: use a WAF/Web Platform (IIS or reverse proxy) to restrict access to potentially vulnreable strings/endpoints.
  • You should probably review vendor guidance (Microsoft)
  • You may want to review your exchange servers for indicators of compromise (IOCs)
  • Check log files for activity, Check for dropped webshells, Check process logs (if you have them!)
  • Microsoft Recomends using the URL re-write module see (Customer Guidance for Reported Zero-day Vulnerabilities in Microsoft Exchange Server – Microsoft Security Response Center

New Microsoft Exchange zero-days actively exploited in attacks (bleepingcomputer.com)

Upcoming | Zero Day Initiative

Upcoming | Zero Day Initiative

Warning: New attack campaign utilized a new 0-day RCE vulnerability on Microsoft Exchange Server | Blog | GTSC – Cung cấp các dịch vụ bảo mật toàn diện (gteltsc.vn)

Read more: Exploitation of Microsoft Exchange Servers seen in the wild

Global Attack Surface

https://www.shodan.io/search/report?query=http.title%3Aoutlook+exchange

There are 201,995 Exchange Servers with Outlook Web Access Exposed (According to Shodan)

cve-2021-31206 (19,311)
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-31206

9.5% of the worlds Exchange attack surface is vulnerable to CVE-2021-31206

PROXYSHELL

https://www.cisa.gov/uscert/ncas/current-activity/2021/08/21/urgent-protect-against-active-exploitation-proxyshell

CVE-2021-34473 (4388)
CVE-2021-34523 (4388)
CVE-2021-31207 (4388)

2.1% of the worlds Exchange attack surface is vulnerable to ProxyShell CVEs (above) (based on the shodan data)

https://learn.microsoft.com/en-us/exchange/new-features/updates?view=exchserver-2019

Exchange CU Versions

IMPORTANT: Your NEED the LATEST Cummualative Update (CU) and the LATEST Security Updates (SU) for Exchange (and given this is a likely zero day scenario you will need to patch again when the latest patches are released from MS)

https://learn.microsoft.com/en-us/exchange/new-features/updates?view=exchserver-2019

Exchange 2019 CU12 Aug22SU

https://support.microsoft.com/en-gb/topic/description-of-the-security-update-for-microsoft-exchange-server-2019-and-2016-august-9-2022-kb5015322-86c06afb-97df-4d8f-af88-818419db8481

Exchange 2016 CU 23 Aug22SU

https://learn.microsoft.com/en-gb/Exchange/new-features/build-numbers-and-release-dates?view=exchserver-2019

https://support.microsoft.com/en-gb/topic/description-of-the-security-update-for-microsoft-exchange-server-2019-and-2016-august-9-2022-kb5015322-86c06afb-97df-4d8f-af88-818419db8481

Exchange Server 2013 CU23 Aug22SU

https://support.microsoft.com/en-gb/topic/description-of-the-security-update-for-microsoft-exchange-server-2013-august-9-2022-kb5015321-96a47598-09b7-43eb-98bb-76fdf906f265

https://www.microsoft.com/en-us/download/confirmation.aspx?id=58392

Summary

The situation appears to be evolving, as always security vulnerabilities and in the wild exploitations can be a fast moving landscape, internet facing systems need suitable and adequate protections, that doesn’t include just exposing IIS on TCP 443 and walking away. It requires capabilities such as:

  • WAF/CDN
  • DoS/DDoS Defence Considerations
  • Logging and Alerting
  • Staff to monitor and respond
  • Secure Configurations
  • Antirivurs/Antimalware
  • Segemntation
  • Endpoint Detection and Response Capabilities (EDR)
  • Incident Response Planning
  • Threat Intelligence

and many more things!

This post is a fast publish and may contain errors and/or the situation may change. I’ll try and keep it updated.

Defense

vSphere Unauthenticated Remote Code Execution Vulnerability – VMSA-2021-0002

For vendor guidance please see:

https://www.vmware.com/security/advisories/VMSA-2021-0002.html

CVE Refs: CVE-2021-21972, CVE-2021-21973, CVE-2021-21974

Introduction

There’s a new unauthenticated remove code execution (RCE) in vSphere 6.5, 6.7 and 7.0 which has just dropped. There’s a vendor patch and currently there is no known public exploit however the hunt will now be on and I can imagine that it’s hours and days until this is in the wild rather than weeks or months.

Read more “vSphere Unauthenticated Remote Code Execution Vulnerability – VMSA-2021-0002” →

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