Ghost

Gbhackers •Divya • June 9, 2026

A newly disclosed “Ghost-Sender” flaw is exposing Microsoft Exchange Online environments to large-scale email spoofing attacks, allowing threat actors to bypass standard email authentication controls and deliver forged messages directly to users’ inboxes. The issue, identified by security researchers Lucas Dodgson, Tobias Oberdörfer, and Robin Hilber, stems from misconfigurations in hybrid or cloud email deployments […]

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Microsoft Exchange 'Ghost-Sender' Flaw Enables Widespread Email Spoofing A newly identified vulnerability in Microsoft Exchange, termed 'Ghost-Sender', allows attackers to spoof any email address, bypassing standard email authentication controls. This flaw affects organizations using Exchange Online or hybrid configurations with third-party mail servers, enabling forged messages to be delivered directly to users' inboxes. Swiss cybersecurity firm InfoGuard reported that this misconfiguration is widespread, with fewer than half of affected organizations applying mitigations. Attackers can impersonate internal and external email addresses, raising the risk of phishing and fraud. Microsoft has acknowledged the issue, with indications that it is being actively exploited. Mitigations include setting up partner organization connectors or creating specific mail flow rules. InfoGuard has also developed a testing tool to help organizations identify vulnerabilities in their configurations. 2 sources 70

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Ghost

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