The XENMEM_exchange handler in Xen 4.2 and earlier does not properly check the memory address, which allows local PV guest OS administrators to cause a denial of service (crash) or possibly gain privileges via unspecified vectors that overwrite memory in the hypervisor reserved range.
Exploitability
AV:LAC:MAu:NImpact
C:CI:CA:C6.9/AV:L/AC:M/Au:N/C:C/I:C/A:C