Microsoft Patches Exploited Exchange Server Vulnerability

Microsoft’s latest Patch Tuesday updates resolve an actively exploited Exchange Server vulnerability tracked as CVE-2026-42897. The tech giant warned Exchange users about zero-day attacks exploiting CVE-2026-42897 on May 14, when it provided temporary mitigations. CISA added the security hole to its Known Exploited Vulnerabilities (KEV) catalog on May 15, instructing federal agencies to address it by May 29. The vulnerability is a spoofing and XSS flaw that impacts Exchange Server Subscription Edition, 2016, and 2019.  “An attacker could exploit this issue by sending a specially crafted email to a user. If the user opens the email in Outlook Web Access and certain interaction conditions are met, arbitrary JavaScript can be executed in the browser context,” Microsoft said in its advisory. The company released patches for the vulnerability on June 9 and urged customers to install the security updates as soon as possible.   Microsoft learned about the vulnerability from a researcher who requested anonymity, and it’s still unclear who is behind the attacks or who the targets are. CISA’s KEV catalog includes two dozen Exchange vulnerabilities, and the data shows that while exploitation surged between 2021 and 2023, no new entries were added to the catalog in 2025, and only CVE-2026-42897 has been added so far in 2026. This indicates that Exchange exploitation is significantly less common today than during the peak years. Related: New Windows Zero-Day Exploit ‘RoguePlanet’ Released Related: ServiceNow Patches Vulnerability Exploited Against Some Customers Related: No Patch Planned for Exploited Arista EOS Vulnerability WRITTEN BY Eduard Kovacs Eduard Kovacs (@EduardKovacs) is senior managing editor at SecurityWeek. He worked as a high school IT teacher before starting a career in journalism in 2011. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering. 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