How Cybercriminals Are Using Trusted Email Security to Bypass Microsoft 365 Defenses

Cybercriminals are once again redefining the threat landscape, this time by exploiting trusted email security mechanisms to compromise Microsoft 365 accounts. In a sophisticated new campaign, threat actors have weaponized link-wrapping services—previously considered pillars of safe email communication—to slip through the cracks of even the most diligent corporate defenses. The result is a fresh wave of phishing that targets organizations worldwide and raises serious questions about the reliability of contemporary email protection solutions.

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Background​

Modern email security is built on layers of defense, with link-wrapping services playing a central role. Provided by major vendors such as Proofpoint and Intermedia, these tools work by replacing potentially unsafe URLs in emails with secure, monitored links that promise to block access to malicious destinations. Historically, this has been an effective shield against low-effort phishing. However, cloud security researchers have confirmed an alarming new trend: attackers are now turning these same shields into attack vectors.
According to incident analyses conducted by Cloudflare, the wave of phishing attacks observed from June through July meticulously leveraged link-wrapping as a cloak for malicious intent. Notably, these campaigns used hijacked accounts already validated by the same security platforms meant to protect them, making it remarkably difficult for detection engines and users to spot anomalies.

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Anatomy of the Attack​

Multi-Layered Deception​

The hallmark of this campaign is its abuse of multi-tiered redirect abuse. Cybercriminals kickstart the process by compromising an email account within a protected environment. With legitimate access, they manipulate link-shortening services to generate a first layer of obfuscation for crisis-laden URLs—those leading to fraudulent login prompts or malware.
As these links are inserted into outgoing messages from trusted sender addresses, the enterprise email security platform, fulfilling its standard protocol, wraps each URL with its own branded, supposedly safe redirector. This produces a chain of redirects, all originating from legitimate-seeming domains. Not only does this streamline the path to the attacker's final site, but it also provides a convenient mask for anti-phishing filters and end-users alike.

Realistic Lures Mimicking Microsoft 365​

These messages tend to imitate high-urgency scenarios, such as missed voicemails, urgent Microsoft Teams notifications, or encrypted communications like those allegedly delivered from “Zix.” In one prominent example, recipients found themselves on a spoofed Constant Contact landing page after clicking what appeared to be a benign link to a secure message.
Often, the attack flow required nothing more than a single click—sometimes on a reply button within a fake Teams alert—for the victim to be directed straight to a convincing Microsoft 365 credential-harvesting portal.

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The Security Consequence of Trust​

Trusted Services as the New Attack Surface​

The danger emerges from an irony of modern cybersecurity: the very tools meant to instill confidence and safety are now regular participants in successful breaches. When users see a familiar security vendor’s domain in a link, and when filters recognize the chain as “safe,” vigilance naturally erodes.
Some of the key trust factors now exploited by attackers include:

• Recognizable sender domains, especially hijacked but legitimate accounts
• Wrapping and redirection URLs from industry-leading security providers
• Emails written in near-flawless corporate vernacular, referencing real productivity services and platforms

This development amplifies the existing risk posed by the abuse of legitimate platforms—think personal cloud storage or document collaboration tools—by adding a double layer of validation through well-known security brands.

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Technical Dissection​

The Chain of Compromise​

• Account Takeover: Attackers first gain access to an email account within an organization using classic phishing, credential stuffing, or buy-in-the-dark-web tactics.
• Link Shortening: They generate a shortened URL pointing to a phishing site designed to mimic the Microsoft 365 login experience.
• Link Wrapping: The compromised account is used to send out mass emails; security platforms automatically wrap the rogue URL, creating a nested structure.
• Obfuscation & Distribution: End recipients see only familiar, security-branded links. Clicking any call-to-action launches them through a series of trusted redirects that ultimately end at the attacker’s credential-harvesting page.

Detection Evasion​

This method sidesteps typical defense-in-depth measures such as:

• Domain-based filtering (since domains reflect trusted intermediaries)
• Heuristic and pattern-based scanning (due to legitimate sender accounts and communication context)
• User training, as the cues that would normally suggest a phishing attempt are now masked by endorsements from well-known services

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Why This Tactic Works​

Psychological Safety Trap​

Human factors play a significant role. Users are trained to look for suspicious links and unfamiliar sender addresses, but few are equipped to scrutinize a URL wrapped by Proofpoint or Intermedia—especially if it originates from a colleague’s real account.

Blind Spots in Automated Security​

Automation and efficiency have ushered in vulnerabilities. Most email security platforms focus on blocking outright threats, not multi-tiered obfuscated traffic that first appears safe. The attacker’s exploitation of access to a protected account sidesteps behavioral anomaly detection, while layered URL rewriting reduces the likelihood of flagging suspicious redirects.

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Notable Strengths of the Attack​

• Effective Bypassing: Even enterprises with advanced filtering and security awareness programs found these attacks difficult to detect.
• Rapid Proliferation: Once inside a trusted domain, phishing campaigns can spread rapidly through internal networks and external partners.
• Reduced User Scrutiny: Multiple layers of trust—familiar sender and recognizable, security-themed links—lower the guard of most users.
• Resilience Against Removal: Since the attack leverages built-in security mechanisms, even blacklisting the final phishing page may not address the fundamental exploit.

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Potential Risks and Implications​

Widening the Attack Surface​

The success of these campaigns signals broader dangers for organizations that over-rely on automated link filtering. Attackers probing the boundaries of trust could soon adapt similar tactics to:

• Bypass zero-trust policies through hijacked badge accounts and embedded collaboration links
• Exploit other forms of content security preprocessing, including attachment sandboxes or web proxies

Exploitation at Scale​

The fact that this technique exploits widely used security layers means any organization connected to Microsoft 365, especially those using industry-standard link-wrapping, is potentially vulnerable.

Credential Compromise Fallout​

Successful theft of Microsoft 365 credentials gives attackers access to a treasure trove of sensitive documents, internal conversations, and downstream applications—escalating the likelihood of business email compromise (BEC), data leakage, and further credential stuffing attacks against other services.

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Defensive Recommendations​

Modernizing Phishing Protection​

Enterprises must adopt multi-faceted security strategies that acknowledge the limitations of automated link-wrapping. Practical steps include:

• Zero-Trust Reviews: Reevaluating policies for trusted services and accounts, applying least privilege principles even to supposedly safe domains
• Out-of-Band Analysis: Leveraging sandbox execution and behavioral analytics on all email content, including links wrapped by trusted services
• Continuous Awareness Training: Updating training programs to highlight how attackers can spoof security services and exploit psychological trust

Technical Safeguards​

• Enhance monitoring for unusual redirect chains, especially those originating from reputable security providers
• Deploy solutions that can inspect and detonate links in real time—even within nested or wrapped contexts
• Partner with link-wrapping vendors to accelerate response and sharing of intelligence on emerging threats

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Cloud Providers and Vendor Responsibility​

Response from Security Vendors​

Vendors like Proofpoint and Intermedia face urgency in adapting their link-wrapping products to detect and disrupt such exploit chains. Solutions under development reportedly include:

• Smarter link-following engines to trace the true final destination of any redirect chain
• AI-powered analysis modules capable of evaluating context and intent, rather than simply validating wrapper URLs
• Faster mechanisms for revoking or blocking malicious chains once discovered in the wild

Microsoft’s Evolving Role​

Given the overwhelming reliance on Microsoft 365, Microsoft is expected to further invest in adaptive threat intelligence, anomaly detection, and automated threat response—especially when credential harvesting campaigns bypass conventional Exchange Online Protection thresholds.

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The Broader Context: Phishing in the Age of Trusted Automation​

Historical Precedent​

Exploiting trust is not new. Attackers have previously abused cloud infrastructure, legitimate file-sharing links, and content delivery networks. The difference now is the weaponization of automated security utilities—a critical evolution that threatens even the most forward-thinking security architectures.

What Comes Next​

Security researchers caution that similar campaigns are likely to escalate in scope and sophistication, leveraging AI to generate even more convincing lures and automate the abuse of protective features. Expect continued attacks against layered security products and persistent innovation around social engineering delivery methods.

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Conclusion​

The abuse of link-wrapping services as phishing enablers marks a pivotal shift in modern cyber threats. As attackers exploit the boundaries of trust and automation, organizations must rethink their approaches to defense, focusing on layered protections that account for human, technical, and procedural weaknesses.
No security tool—however trusted or familiar—should be considered invulnerable. The episode stands as a timely reminder: confidence in security must always be matched by continuous vigilance and critical scrutiny of every link, sender, and notification, no matter its surface appearance. As the arms race between defenders and cybercriminals intensifies, adaptability and skepticism are the keys to staying one step ahead.

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Source: Windows Report Hackers abuse link-wrapping to steal Microsoft 365 credentials