Microsoft Reports Severe Zero-Day Flaw in On-Prem Exchange Servers
The zero-day vulnerability affects on-premises installations for all versions of Exchange Server 2016, 2019 and Subscription Edition
Stay updated on Exchange Server security with the latest news, updates, and expert insights into protecting your email communications effectively.
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Background for this topic.
Exchange Server is a Microsoft server platform for organizational email, calendars, contacts, and mailbox storage. It may run within an organization or as part of a hybrid environment, and commonly exposes web, mail-transfer, and administration interfaces. Because it stores business communications and can mediate access to accounts, it is a high-value system for security teams.
Security concerns include exploitation of vulnerabilities in internet-facing services, theft or misuse of privileged accounts, and unauthorized mailbox access through weak authentication or compromised credentials. Protection requires prompt, tested security updates; minimizing and monitoring external exposure; strong authentication for administrators and remote access; and careful separation of administrative privileges. Logs from web access, authentication, mailbox activity, and mail flow support detection and investigation. Organizations should also maintain tested backups and recovery procedures, while applying retention, access-control, and privacy requirements to stored messages and attachments.
The zero-day vulnerability affects on-premises installations for all versions of Exchange Server 2016, 2019 and Subscription Edition
On Thursday, Microsoft shared mitigations for a high-severity Exchange Server vulnerability exploited in attacks that allow threat actors to execute arbitrary code via cross-site scripting (XSS) while targeting Outlook on the web users. [...]
Microsoft has disclosed a new security vulnerability impacting on-premise versions of Exchange Server that it said has come under active exploitation in the wild