Introduction

Details of a critical vulnerability impacting Microsoft’s Exchange 2013 and 2016 servers were recently discovered and made public.  If successfully exploited this vulnerability would allow an attacker to gain Domain Admin permissions within a company’s Active Directory infrastructure allowing nearly unrestricted access to a compromised server.  At this time Microsoft has not released a patch for this vulnerability.  Tier1Net customer’s which have implemented Tier1Net’s Cisco Umbrella Secure DNS and/or Duo Authentication services have their exposure to this vulnerability greatly reduced.

Technical Information

In order to successfully exploit this vulnerability an attacker would first need to gain the credentials to any existing mailbox on a targeted Exchange server.  This can be accomplished via phishing attacks or credential stuffing where an attacker uses breached credentials from one service to gain access to another service.  Once an attacker has access to a mailbox on the Exchange server they can then combine three known vulnerabilities to elevate the compromised account’s permissions to that of a Domain Admin.   A Domain Admin has full access to an Exchange server and can perform such tasks as resetting password, creating mailboxes, deleting mailboxes, etc.

Steps Being Taken by Tier1Net

Due to Tier1Net’s expertise and emphasis on cybersecurity, many of its customers are already protected from this latest vulnerability.  Furthermore, Tier1Net deploys multiple security layers to both its own internal and hosted infrastructures as well as client supported networks to greatly reduce the exploit risk of any single vulnerability.  To further reduce customer exposure to this vulnerability Tier1Net will be deploying a Microsoft supported mitigation tool to all managed and hosted Exchange servers.

Additional Information

https://dirkjanm.io/abusing-exchange-one-api-call-away-from-domain-admin/
https://nakedsecurity.sophos.com/2019/01/30/privilege-escalation-vulnerability-uncovered-in-microsoft-exchange/
https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2018-8581