Due to the MS13-061 security bulletin, all currently supported versions of Exchange got a Security Update or a Rollup Update which also includes the security update.
Due to an issue with the installer, the original updates for Exchange 2013 were pulled but are now available again as a v2 release.
If you had already applied the original release to Exchange 2013, there are additional steps which you must take to correct the issue.
The vulnerabilities exist in the WebReady Document Viewing and Data Loss Prevention features of Microsoft Exchange Server. The vulnerabilities could allow remote code execution in the security context of the transcoding service on the Exchange server if a user previews a specially crafted file using Outlook Web App (OWA).
The Rollup Updates also includes a few additional fixes, so make sure you review their corresponding KB article too before applying them.
View: MS13-061 security bulletin
View: Exchange Team Blog Post about these updates
Download: Update Rollup 11 for Exchange Server 2007 Service Pack 3 (KB2873746)
Download: Update Rollup 7 for Exchange Server 2010 Service Pack 2 (KB2874216)
Download: Update Rollup 2 For Exchange 2010 SP3 (KB2866475)
Download: Security Update v2 For Exchange Server 2013 CU1 (KB2874216)
Download: Security Update v2 For Exchange Server 2013 CU2 (KB2874216)