A critical security flaw in Proofpoint’s email routing infrastructure has been exploited in a large-scale phishing campaign, affecting millions of users. The vulnerability, identified by cybersecurity firm Guardio Labs, allowed threat actors to send spoofed emails impersonating major companies such as Best Buy, IBM, Nike, and Walt Disney. These emails, which were routed through Proofpoint’s servers and bore authentic SPF and DKIM signatures, managed to bypass conventional security measures, making them appear credible and deceiving recipients into divulging sensitive information.
The campaign, named “EchoSpoofing,” began in January 2024 and quickly escalated, with the attackers sending up to 14 million spoofed emails per day by early June. The technique involved leveraging a misconfiguration in Proofpoint’s email routing settings, which permitted emails from adversary-controlled Microsoft 365 tenants to be relayed through Proofpoint’s infrastructure. This misconfiguration enabled the attackers to bypass standard authentication checks and deliver phishing emails that appeared to come from legitimate domains.
Guardio Labs’ report highlights that the flaw allowed the attackers to use a rotating series of leased virtual private servers (VPS) and multiple IP addresses to send bulk messages. This sophisticated method made it difficult for recipients to discern the spoofed emails from genuine communications. Proofpoint has since responded by implementing a streamlined administrative interface to control which Microsoft 365 tenants are allowed to relay emails, aiming to prevent similar exploitation in the future.
Despite the scale of the attack, Proofpoint has confirmed that no customer data was exposed or lost as a result of the phishing campaign. The company has taken steps to notify affected customers and has urged email service providers and VPS operators to tighten their controls to prevent such abuses. As cybersecurity experts stress the importance of rigorous email security measures, Proofpoint’s experience underscores the need for vigilance in safeguarding email infrastructures against sophisticated phishing tactics.
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