Microsoft says that four of the bulletins (MS13-096, MS13-098, MS13-104 and MS13-106) contain a vulnerability which is being exploited in the wild. Of particular concern is MS13-098 which could undermine code signing, one of the more important fundamental protections available today.
MS13-104: Vulnerability in Microsoft Office Could Allow Information Disclosure (2909976) — By getting a user to open an Office document on a malicious web site, the attacker could ascertain access tokens used to authenticate the current user on a targeted SharePoint or other Microsoft Office server site. Strangely, Microsoft says both that functional exploit code for this vulnerability is unlikely, and that they are aware of limited, targeted attempts to exploit it. [UPDATE: Thanks to @NoamLiran for pointing me to the exploit research for this vulnerability. I asked Microsoft how the index could be 3 and they replied that "The Exploitability Index only attempts to rate vulnerabilities that can be leveraged for code execution. Vulnerabilities that could allow denial of service, tampering, information disclosure or spoofing will receive an Exploitability Index rating of '3.' The notes for that particular CVE will also reflect the nature of the vulnerability." Click here for Microsoft's rules for the Exploitability Index.]