In contemporary cyberattacks, email continues to be the main initial access vector. In 27% of reported breaches, email was the first attack vector, and 60% of all breaches involved some kind of human element, according to Verizon's 2025 Data Breach Investigations Report. However, traditional phishing attacks have become more difficult with the use of AI-driven spam filters and authentication protocols like SPF, DKIM, and DMARC.

However, what occurs if hackers get past these email security safeguards? The solution is to take advantage of email vulnerabilities, particularly by abusing email endpoints and exposing OAuth tokens. The Abuse of Email Endpoints Contemporary web applications frequently reveal communication endpoints that are necessary for valid business operations like password resets and newsletter signups.

These endpoints could, however, turn into a vulnerability if they are not implemented properly. For example, a public-facing API for newsletter subscription could let hackers send emails through a company's authentic email system, getting around security measures like DMARC, DKIM, and SPF. OAuth Weakness Is Used by Phishing (Source: Praetorian) Attackers can use this feature as a weapon to send phishing emails that look like they are coming from reliable sources.

This method makes it simple for phishing emails to get past security measures. They are highly convincing because they may show the company's official email address and even show up in the recipient's primary inbox with a tag that reads "Important." The Exposure of Tokens Verbose error handling is the source of the second vulnerability.

Error responses in many contemporary applications can provide comprehensive system details, including authentication tokens for vital services like Microsoft 365. Attackers can obtain authenticated access to organizational resources without causing the usual failed login alerts when OAuth tokens are made public in this way.

OAuth Weakness Is Used by Phishing (Source: Praetorian) Praetorian claims that OAuth tokens used for authentication, especially those for the Microsoft Graph API, can give hackers access to private information like: User profiles with contact details, job titles, and names The ability to send and receive emails that may contain malware SharePoint and OneDrive files and documents Microsoft Teams chats, calendar data, and meeting details Phishing Attacks Weakness of OAuth (Source: Praetorian) The vulnerabilities discussed here show how even medium-severity flaws can have disastrous results if they are combined. To find possible flaws before attackers do, organizations must routinely evaluate their web applications and error-handling protocols by modeling actual attacks.

Security teams can lower the risk of exploitation and protect vital systems by adopting an adversarial mindset and carrying out in-depth security assessments.