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Exchange Server update permanently removes OWA Light and exposes a hybrid

Feeds.4Sysops •IT News • August 12, 2026

Microsoft’s August 2026 Exchange Server security update permanently disables the legacy OWA Light client on every server that installs it. The release also leaves a known hybrid-deployment problem affecting messages sent from shared mailboxes, giving administrators two important post-update checks. Source

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Exchange Server August 2026 Update Disables OWA Light and Addresses Vulnerabilities Microsoft's August 2026 Exchange Server security update permanently disables the OWA Light client across all servers. This update addresses an authentication-bypass vulnerability demonstrated at Pwn2Own, affecting Exchange Server 2016 and 2019. Organizations must be enrolled in Period 2 Extended Security Updates to continue receiving updates. Additionally, the update exposes a hybrid-deployment issue impacting messages from shared mailboxes, requiring administrators to conduct post-update checks. The vulnerabilities could potentially allow unauthorized access to sensitive information if not addressed. The update is critical for maintaining security in affected systems, and organizations are urged to apply it promptly. 2 sources 71

Extracted Entities

Platforms (1)

Microsoft Exchange Server