The Xen security team has released three security advisories regarding the Xen hypervisor. AWS customers are not affected by these issues.
Information on the advisories can be found below:
Xen Security Advisory 7 (CVE-2012-0217) - PV privilege escalation
Xen Security Advisory 8 (CVE-2012-0218) - syscall/enter guest DoS
Xen Security Advisory 9 (CVE-2012-2934) - PV guest host DoS (AMD erratum #121)