Some vulnerabilities have been reported in Xen, which can be exploited by malicious, local users to cause a DoS (Denial of Service) or bypass certain security restrictions.
1) An error within the handling of the DR7 debug register can be exploited out of a guest system to crash the hypervisor by setting certain breakpoints.
Successful exploitation may require that a HVM hypervisor is used.
2) Access to the CR4 register is not properly checked. This can be exploited out of a guest system to e.g. crash DomU or Dom0 domains.
Successful exploitation may require that a paravirtualised kernel is used.
3) The ioemu block device backends do not properly check a HVM guest's read or write attempts, which can be exploited out of a HVM guest system to e.g. crash Xen or potentially escape the virtualisation jail by writing into arbitrary Dom0 memory.
Note: Successful exploitation requires privileges to send specially crafted read or write requests to the ioemu block device driver backends.
4) An error exists in the PVFB (Para Virtualized Frame Buffer) functionality while processing screen update requests. This can be exploited to cause a crash or potentially execute arbitrary code in a Dom0 domain.
Solution: Update to version 3.2.1, which fixes vulnerabilities #3 and #4.
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Subject: Xen Multiple Vulnerabilities
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