This threat involves threat actors leveraging complex email routing paths and misconfigurations within an organization's email infrastructure to spoof legitimate domains. By doing so, phishing emails can appear as though they are sent internally, bypassing common email security filters and increasing the likelihood of successful phishing attacks. The attackers exploit weaknesses in how email forwarding, relaying, and domain authentication protocols such as SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting & Conformance) are configured or enforced. Misconfigured routing can allow emails to pass SPF or DKIM checks erroneously or cause DMARC policies to fail, enabling spoofed emails to reach end users with a high degree of trust. This technique does not depend on software vulnerabilities but rather on operational security gaps in email infrastructure management. The absence of known exploits in the wild suggests this is an emerging or underreported tactic. The medium severity rating reflects the moderate impact on confidentiality and integrity, as successful phishing can lead to credential compromise or malware deployment, but exploitation requires some level of user interaction (opening or acting on the email). The threat is particularly relevant for organizations with complex or hybrid email environments, including those using multiple email gateways, forwarding rules, or cloud-based email services. Attackers can leverage these complexities to evade detection and impersonate internal senders convincingly.

For European organizations, the impact of this threat can be significant, especially for large enterprises and public sector entities that rely on complex email infrastructures and have high volumes of internal communications. Successful domain spoofing in phishing attacks can lead to credential theft, unauthorized access to sensitive systems, data breaches, and potential financial fraud. The perceived legitimacy of emails appearing to come from internal sources increases the risk of users disclosing confidential information or executing malicious attachments or links. This can undermine trust in internal communications and disrupt business operations. Additionally, regulatory requirements such as GDPR impose strict obligations on protecting personal data, and phishing-induced breaches could result in substantial fines and reputational damage. Organizations with hybrid or multi-cloud email environments may face greater challenges in securing routing configurations, increasing their exposure. The threat also complicates incident response, as spoofed internal emails can mislead security teams and delay detection.

To mitigate this threat, European organizations should conduct comprehensive audits of their email routing configurations to identify and correct misconfigurations that could be exploited for domain spoofing. Implementing and enforcing strict SPF, DKIM, and DMARC policies is critical; organizations should ensure that these protocols are correctly configured to cover all legitimate sending sources and that DMARC policies are set to quarantine or reject unauthorized emails. Regularly monitoring DMARC reports can help detect unauthorized use of domains. Organizations should minimize complex forwarding rules and avoid unnecessary email relays that complicate authentication checks. Deploying advanced email security solutions that analyze email headers and routing paths can help detect anomalies indicative of spoofing. User awareness training should emphasize the risks of phishing emails that appear internal and encourage verification of unexpected requests. Incident response plans should include procedures for handling suspected internal spoofing attempts. Collaboration with email service providers and security vendors can assist in maintaining robust email security postures.