This emerging phishing campaign exploits the widespread use of Microsoft and Google Calendar invites within corporate environments by sending fake calendar invitations designed to steal login credentials. The attackers employ email spoofing techniques to impersonate trusted senders and create a sense of urgency with fake meeting requests, increasing the likelihood of user interaction. The phishing emails contain embedded links or buttons that redirect victims to fraudulent login pages that closely mimic the official Microsoft or Google authentication portals, thereby deceiving users into submitting their credentials. The campaign leverages the routine and trusted nature of calendar invites to bypass typical user skepticism and security controls. Multiple malicious domains and IP addresses have been identified as part of the infrastructure supporting these attacks, indicating a coordinated effort. Although no direct software vulnerabilities are exploited, the campaign relies heavily on social engineering tactics (MITRE ATT&CK techniques T1566, T1204, T1036) and credential theft (T1078). The threat actors have not been publicly identified, and no known exploits in the wild have been reported to date. The campaign's sophistication lies in its mimicry of legitimate platforms and exploitation of business workflows, making detection challenging without user awareness and technical controls. References include detailed analysis from Cofense and AlienVault OTX. The threat is ongoing and requires proactive defense measures.

The primary impact of this calendar phishing campaign is the compromise of user credentials for Microsoft and Google accounts, which can lead to unauthorized access to corporate email, documents, and other sensitive resources. Credential theft can facilitate further attacks such as business email compromise (BEC), data exfiltration, lateral movement within networks, and deployment of malware or ransomware. Organizations relying heavily on Microsoft 365 or Google Workspace are particularly at risk, as compromised credentials can undermine the security of cloud services and collaboration tools. The social engineering nature of the attack means that even well-secured environments can be vulnerable if users are not adequately trained. The campaign can disrupt business operations, cause financial losses, and damage organizational reputation. Additionally, stolen credentials may be sold or used in subsequent attacks, increasing the long-term risk. The medium severity rating reflects the significant potential for harm balanced against the requirement for user interaction and the absence of direct exploitation of software vulnerabilities.

To mitigate this threat, organizations should implement targeted user awareness training focusing on the risks of calendar invite phishing and the importance of verifying sender details and meeting legitimacy. Deploy advanced email filtering solutions capable of detecting and blocking spoofed emails and malicious links, including domain-based message authentication, reporting, and conformance (DMARC), SPF, and DKIM enforcement to reduce email spoofing. Enable multi-factor authentication (MFA) on all user accounts to limit the impact of credential compromise. Configure calendar applications to restrict automatic addition of calendar invites from unknown senders or to flag such invites for user review. Employ URL filtering and sandboxing technologies to detect and block access to known phishing domains and URLs identified in this campaign. Regularly update threat intelligence feeds with indicators of compromise (IOCs) such as the listed malicious domains and IP addresses to enhance detection capabilities. Conduct phishing simulations to test and reinforce employee vigilance. Finally, establish incident response procedures to quickly address suspected credential theft and unauthorized access.