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Phishing Attacks via Microsoft Exchange: Prevention and Response. Phishing assaults have grown more complex in recent years, which presents severe obstacles to enterprises’ cybersecurity plans. With the proliferation of Microsoft Exchange servers as a cornerstone of communication and collaboration within enterprises, these platforms have emerged as prime targets for malicious actors seeking unauthorized access and sensitive data. This article explores the evolving landscape of phishing attacks targeting Microsoft Exchange servers, focusing on effective prevention measures and proactive response strategies to mitigate risks and safeguard organizational assets.

Phishing Attacks via Microsoft Exchange: Prevention and Response

Since phishing attacks are the second most frequent attack vector, it is necessary to have a strategic incident response procedure in place to reduce and manage any associated risks. It’s getting more challenging to determine whether we have fallen victim to phishing assaults due to their increasing intricacy. Whether we are just beginning to suspect the attack or are in the middle of validating it, it will be in our organization’s best interest to take immediate action.

Phishing attacks, while varied in their execution, often stem from several common underlying causes. Organizations must comprehend these elements to strengthen their defenses against such attacks successfully.

Some of the most prevalent causes:

  1. Exploiting Human Vulnerabilities: Phishers exploit human weaknesses using social engineering tactics to trick individuals into divulging personal information or clicking malicious links.
  2. Weak Authentication Practices: Inadequate authentication methods, such as easily guessable passwords or the absence of multi-factor authentication (MFA), enable attackers to compromise user accounts and conduct phishing attacks.
  3. Vulnerabilities in Software and Systems:  attackers may infiltrate networks and deploy phishing tactics.
  4. Lack of Employee Training and Awareness: organizations are vulnerable and increase their risk of data breaches or financial losses.
  5. Inadequate Email Security Measures: Poor email security (email filtering or domain authentication protocols) raise the chances of phishing emails reaching users’ inboxes, heightening susceptibility to phishing attacks.

Microsoft Exchange Phishing Prevention

With the frequency of data breaches and the increasing cost of ransom, cloud security becomes a crucial business need to defend our data, users, and whole organizations against cloud risks. Implementing the appropriate incident response plan and utilizing technologies that decrease risks and improve procedures are crucial to swiftly and efficiently identify and eliminate various types of malware.

Use these resources to bolster security and swiftly respond if it reoccurs.

Additional Phishing Prevention for M365

Supplementary measures to bolster anti-phishing defenses external to Microsoft products:

Following Microsoft’s best practices to help us, our organization, and our users to be more prepared and protected against these ever-growing attacks.

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Microsoft Exchange Phishing Responses

We have limited time to clean and secure our environment after the malware infects it. The risk of data loss, increased ransom fees and a wider spread of infection increases with the time the attacker has access to our data and credentials. Follow these procedures, which are essential if an infection is suspected.

Responses as a User

As users, we must understand that a phishing attack affects the whole organization. 

Best practice would be to quickly inform our management team about the attack (or the suspicion), so administrators enforce rules and policies to minimize the risks of the breach.

Responses as an Administrator

Before recovering lost data, the goal is to stop the infection and regain control of our Exchange 365 email account and related apps. Take the following actions to start taking back control:

Regain Email Access

Initially, any unauthorized access must be eliminated and prevented from leading to any further illegal activity that might compromise, steal, or destroy our data. Do this by:

  1. Reset the user’s password. The new password must be secure, safe, and complicated, requiring capital and lowercase numbers and special characters. Please do not send the new password to the email of the intended user, as we are still in the primary step of regaining control over the email account.
  2. Remove suspicious email forwarding addresses. This would ensure we only allow and send legitimate and trusted accounts to emails. When we remove specific addresses, we are not letting those accounts receive forwarded emails from the compromised account.
  3. Disable suspicious inbox rules. To ensure that while we fix the account, no automated actions are performed, such as automatically forwarding email messages to another account.
  4. Unblock the user from sending mail. Microsoft immediately marks the mailbox as restricted if the attacker utilizes the email address to send spam. It will not allow it to send any more messages.
  5. Block user account from signing in. Until we secure the account safely with no unwanted access, continue to block any attempt to sign into the account.
  6. Remove the account’s administrative roles to avoid unwanted control over other accounts. Do this via:

Take back control in these areas because Exchange Online syncs across apps and devices and is firmly integrated with the other Microsoft 365 capabilities. Stopping updates and syncs would prevent the potential spread of data encryption. To accomplish this, we can:

  • Deactivate Exchange ActiveSync for a mailbox to cease data syncing between devices and Exchange Online mailboxes.
  • Temporarily suspend OneDrive sync to halt updates of cloud data from infected devices.

Run Antivirus Scan

As we temporarily suspend access to our mailbox access, conducting a comprehensive antivirus scan on suspected computers and devices, including those synchronizing data, is appropriate.

Use two native Microsoft tools for detection and removal of malware:

Recover Files and Emails

Once we determine that our environment is safe from malware payload or unwanted access, we restore our data that’s either encrypted or deleted.

If our backup versions are safe, use:

  • Utilize File History on Windows 11, Windows 10, and Windows 8.1 to attempt the restoration of local files and folders.
  • Employ Files Restore in OneDrive for Business to revert our entire OneDrive to a previous state within a 30-day timeframe.

In cases where we delete all of the users’ emails, we recover deleted items by following this process. Or, if we have a third-party backup solution, restore any file or email data from there.

Reinstate Access and Reenable Sync

Report Message to Microsoft

Microsoft recommends enhancing its email filters and taking preventative measures to avoid recurrence as best practice. Additionally, it advises reporting the attack by submitting emails, attachments, or files. We can do so by following these steps.

Phishing Attacks via Microsoft Exchange: Prevention and Response Conclusion

In conclusion, the threat landscape surrounding phishing attacks via Microsoft Exchange demands a multifaceted approach to prevention and response. While technological solutions such as advanced email filtering and threat detection play a crucial role, organizations must also prioritize continuous employee training and awareness programs to empower users in identifying and thwarting phishing attempts. Additionally, establishing incident response protocols and regularly updating security measures are paramount to effectively mitigating the risks posed by these persistent and evolving cyber threats, ensuring the integrity and confidentiality of organizational data in an ever-changing digital environment.


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Marion Mendoza

Marion Mendoza

Windows Server and VMware SME. Powershell Guru. Currently working with Fortune 500 companies responsible for participating in 3rd level systems support across the enterprise. Acting as a Windows Server engineer and VMware Specialist.

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