microsoft has released a fix for outlook Web app in all supported versions of exchange.
In all cases, it comes to security issues that have been designated as Important.
Four security updates are also those offered by Microsoft update, but here are the manually download links:
Rollup 15 for Exchange Server 2007 Service Pack 3
Rollup 8 for Exchange 2010 SP3
Security Update For Exchange Server 2013 SP1 (KB3011140)
Security Update For Exchange Server 2013 CU6 (KB3011140)
Cumulative Update 7 for Exchange Server 2013 (Provided not with windows Update)
Versions that are not listed here are no longer supported or are not vulnerable. For more information read the security bulletin MS14-075: Vulnerabilities in Microsoft Exchange Server Could Allow Elevation of Privilege (3,009,712)