Protect Your Microsoft 365 from Stealthy Attack Waves Exploiting Trust

Microsoft business users are being alerted to a stealthy and sophisticated wave of attacks exploiting the trust built into official Microsoft 365 notifications. Leveraging the genuine “microsoft-noreply@microsoft.com” address, cybercriminals are injecting malicious content into transactional emails—creating fraudulent billing messages that are highly convincing. As email security filters often rely on sender reputation, these malicious emails are not easily flagged as suspicious, making them uniquely dangerous for enterprise security teams and end users alike.

Anatomy of the Attack: Hijacking Microsoft 365 for Social Engineering​

Recent discoveries by Kaspersky’s threat research team reveal that attackers have abused legitimate Microsoft mechanisms for sending account-related notifications to their targets. The initial email, which appears no different from authentic subscription or purchase confirmations, thanks the recipient for a (fictitious) Microsoft 365 Business subscription purchase. Importantly, the notification includes “billing information” and a contact number, which, rather than belonging to Microsoft, is orchestrated by the scam operators themselves.
“The message easily gets past any email server filters,” notes Kaspersky's spam analysis expert Roman Dedenok, highlighting the significance of the attack coming directly from a trusted Microsoft domain. This lends the email almost unparalleled legitimacy and immediacy, catching employees off guard—especially those who might worry about accidental or unauthorized company expenditures.
The tactics commonly revolve around:

• Generating anxiety by referencing expensive or urgent purchases in the name of the company.
• Blocking easy verification: the no-reply sender address prevents employees from easily confirming the transaction via email.
• Exclusively providing a phone number owned by the attackers as the only point of contact.

When potential victims phone the provided number, the scam escalates: operators perform classic “tech support” maneuvers, insisting that remote support tools be installed. Victims are sometimes sent executable files (.EXE) that likely contain Remote Access Trojans (RATs). A particularly harmful development is the scammers’ request to “process a refund,” instructing the target to sign in to their online banking—inviting credential theft via the backdoor installed software.

How Are the Attackers Sending Official Microsoft Notifications?​

Perhaps the most alarming aspect is the use of bona fide Microsoft notification channels. According to Kaspersky, it remains unclear exactly how attackers are injecting their own billing and support content into these messages. Two primary theories have emerged:

• Stolen Credentials or Misused Trial Licenses: Attackers could acquire valid login details or gain trial access to Microsoft 365. By entering the intended victim’s email address in the BCC field (or as the recipient during a trial sign-up), they ensure the generated billing message is sent directly to the target—complete with malicious substitutions in the contact information.
• Account Takeover with Billing Resend Abuse: If threat actors compromise an account with an active subscription, they may use Microsoft’s own tools to resend billing information, altering the destination address or content as needed to redirect victims into their social engineering pipeline.

No matter the method, these tactics circumvent traditional email screening methods and demonstrate the adaptability of highly motivated cybercriminal groups. The attack represents an advanced form of business email compromise (BEC), but one bolstered by the apparent authenticity of Microsoft as the sender.

The Changing Email Threat Landscape: From BEC to RATs​

Social engineering campaigns via email have been an escalating threat to enterprises worldwide. According to Barracuda’s detailed threat reports, business email compromise attacks accounted for more than 10% of all social engineering-based intrusions in 2023—a marked increase over 8% in 2022 and 9% in 2021. The trendline is unmistakable: attackers are shifting from broad, obvious phishing to highly credible, targeted, and business-focused threats.
Interestingly, while Gmail remains the most commonly used address for social engineering attacks, Microsoft’s ecosystem is especially attractive for “insider” attacks—those abusing notifications, purchase confirmations, or responses to employee actions. The use of official domains increases both the success rate and the potential damage.
Tilly Travers of Barracuda stresses that “IT and security professionals need to understand how the email threat ecosystem is evolving,” noting that modern BEC and supply-chain attacks require organizations to rethink risk management, user resilience, and incident response strategies.

Breaking Down the Attack Flow​

To appreciate the risks posed by this new strain of notification abuse, consider the attack flow:

• Victim Receives Official-looking Microsoft Notification: The email arrives from microsoft-noreply@microsoft.com, confirming a significant business purchase.
• Message Contains Fraudulent Billing and Support Links: Instead of legitimate Microsoft contact information, the message features a scammer-controlled phone number.
• Victim Makes the Call: Motivated by anxiety or workplace responsibility, the employee calls the number, where “Microsoft support” staff walk them through the next steps.
• Installation of Remote Access Tools: The scammer convinces the user to install remote support software, usually an EXE or other executable program, in reality, a RAT.
• Credential Harvesting: Under the guise of processing a refund for the mistaken transaction, the victim is asked to log in to their online banking or enter other sensitive credentials while the RAT is active, exposing login information to the attackers.
• Potential for Lateral Movement and Business-wide Compromise: Once inside the endpoint, attackers can escalate privileges, harvest further data, and potentially move deeper into the organization’s network.

Technical Analysis: Why This Attack is So Effective​

Several factors combine to make this campaign exceptionally dangerous:

1. Abuse of Trusted Notification Channels​

Unlike most phishing attempts that rely on spoofed sender domains or lookalike email addresses, these attacks use Microsoft’s actual notification infrastructure. Email gateways and spam filters are usually configured to explicitly trust messages from domains such as microsoft.com, making these emails far more likely to reach their intended targets.

2. Social Engineering Based on Employee Psychology​

By referencing high-value or expensive purchases, the scam leverages a nearly universal fear among employees: the risk of accidental expenditure (and the potential repercussions). The “no-reply” sender setting prevents easy digital inquiry—funneling the concerned recipient straight to the scammer’s phone number.

3. Remote Access Trojan Deployment​

The support call phase is when technical and social engineering efforts converge. By insisting on remote access installations, attackers attempt to skirt endpoint protection and gain immediate, direct access to a compromised system.

4. Banking and Refund Deceptions​

Manipulating users into logging into online banking while the RAT is active enables attackers to perform real-time credential harvesting and, in some cases, initiate unauthorized transactions.

Possible Attack Vectors for Exploiting Notifications​

The inner workings of Microsoft 365 are not public, so how attackers send altered notifications remains a matter of speculation. Kaspersky’s theories are echoed by several information security experts:

• Test or Trial Subscriptions: By signing up for Microsoft 365 using compromised or forged payment details (or trial sign-ups), attackers can generate “thank you” billing notifications, specifying the target’s actual email address in the purchase flow.
• Account Takeover Attacks: If attackers compromise a legitimate business account, they can exploit Microsoft admin interfaces to resend or modify confirmation emails, embedding scam contact information in the process.
• Third-Party Integrations or API Abuses: While less likely, some suggest attackers might abuse APIs or partner platforms tied to Microsoft’s notification system, though this is still to be demonstrated in the wild.

In the absence of definitive technical public disclosures from Microsoft, these remain probable, but unconfirmed, vectors.

Defenses and Mitigation: What Organizations Can Do​

In the face of these rapidly evolving scams, a layered defense strategy is paramount for businesses using Microsoft 365 and similar cloud-based ecosystems.

User Awareness and Training​

As always, the human factor is the most exploitable aspect of any defense framework. Companies should consider:

• Regular Anti-phishing Training: Ensure all users, especially those in roles that handle purchases or expense management, are familiar with modern phishing and BEC techniques.
• Simulated Phishing Drills: These foster “muscle memory” and vigilance, lowering the likelihood that users will fall for cleverly crafted scams.

Technical Controls​

Mitigation measures include:

• Implementing Advanced Email Security Gateways: Solutions that scan for not only sender authenticity but also anomalous content, links to external numbers, or out-of-character billing details can help flag suspicious emails.
• Endpoint Protection and Behavioral Monitoring: Modern security suites can detect abnormal activity, such as unknown RAT installations or unusual outbound network connections.
• Multi-factor Authentication (MFA): For both Microsoft and banking accounts, MFA disrupts the attacker’s ability to exploit stolen credentials, even if they have been harvested.

Policy and Procedure​

• Mandate Internal Verification: Staff should be instructed to verify major purchases, suspicious emails, or refund communications via known, direct corporate channels—and never solely by responding to contact information embedded within an unexpected notification.
• Limit Administrative Privileges: Restrict who in the organization has the ability to subscribe, configure, or re-send billing details using Microsoft 365’s management tools.

Industry Response and What Needs to Change​

Microsoft has not, as yet, provided a definitive technical explanation or acknowledgments of systemic vulnerabilities related to this attack. The apparent use of their own infrastructure for malicious purposes is a wake-up call: cloud giants must introduce stricter controls and enhanced auditing around automated billing notifications and admin activities.
Kaspersky advises organizations to ensure robust endpoint security and foster a culture of “zero trust” for unsolicited incoming communications—even from the world’s most trusted brands. As reported in IT Pro, the firm also urges companies to deploy comprehensive anti-RAT and anti-spyware solutions to every device, thereby reducing the odds that a single successful scam could lead to a major breach.

Critical Perspective: Strengths, Weaknesses, and the Path Forward​

This notification abuse campaign illustrates both the resilience and risk inherent in today’s cloud-centric workplace:

Strengths of the Attack​

• Credibility: Use of a genuine Microsoft sender domain is almost impossible for recipients—or even many IT controls—to distinguish from standard, safe communications.
• Psychological Targeting: Exploiting employee apprehension about company finances triggers rapid, less-skeptical responses.
• Bypassing Technical Barriers: The blend of email reputation and adaptable social engineering undermines many traditional security layers.

Weaknesses (from a cybercriminal perspective)​

• Resource Intensive: The need for human operators (to answer calls and run tech support scripts) doesn’t scale as easily as fully automated phishing.
• Potential for Attribution: Phone-based and remote support attacks are more traceable than pure email-based exploits, especially if attackers are incautious with infrastructure or operational security.

Emerging Risks​

• Automation of These Tactics: It is likely that, in the future, attackers may automate the creation and injection of malicious content into large batches of notifications.
• Supply Chain Compromise: Attackers may seek to compromise Managed Service Providers (MSPs) or vendor accounts that manage Microsoft 365 for multiple organizations—greatly expanding the reach of their campaigns.

Recommendations for a Safer Microsoft 365 Experience​

• Microsoft should review and restrict how notifications are generated, especially when they originate from administrative or billing functions.
• Adoption of Domain-based Message Authentication (DMARC) policies that regard even minor deviations in message structure or content as suspect.
• Increased visibility for organizations into all outgoing communications using cloud dashboards—flagging unusual activity with built-in machine learning tools.
• User-level controls to suppress or verify certain types of notifications, particularly those referencing financial transactions or changes in account status.

For individual organizations, combining technical security layers with persistent training and awareness is now non-negotiable. Enterprises must treat every “official” notification as a potential vector, confirming even the most credible messages directly with trusted parties—and never via contact points embedded in the notification itself.

Conclusion: Trust, but Always Verify​

The abuse of Microsoft 365’s notification system demonstrates the evolving tactics of cybercriminals focused on trust exploitation. These campaigns bypass many technical security measures by posing as genuine, trusted communications, and push end users into high-pressure scenarios that favor social engineering over technical trickery.
For Windows and Microsoft cloud users, the lesson is clear: robust defense now hinges as much on skeptical human behavior as it does on digital controls. By building a work culture that verifies before trusting, deploying comprehensive endpoint and email security, and demanding greater transparency from cloud service providers, the enterprise can reduce its risk profile—even as attackers grow ever more innovative in their abuse of our most trusted digital platforms.

---

Source: IT Pro Hackers are abusing Microsoft email notifications to target enterprises