UPDATE June 9, 2026: Please see our release blog post for June 2026 Security Update for more information on this CVE: Released: June 2026 Exchange Server Security Updates | Microsoft Community Hub.
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Updated Jun 09, 2026
Version 15.0
Blog Post
Any idea why the EM service logs :
ApplyMitigation,S:LogLevel=Error;'S:Message=Encountered exception while applying mitigation M2.1.0 : Filename: \\?\E:\Exchange Server\V15\FrontEnd\HttpProxy\owa\web.config\r\nError: The configuration section ''system.webServer/rewrite/outboundRules'' cannot be read because it is missing a section declaration\r\n\r\n';S:Source=Microsoft.Exchange.Mitigation.Service.Mitigations.MitigationEngine
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Edit: it appears the rewrite module was installed but not registered in IIS... Launched a repair of the msi and it reappeared then the mitigation applied.