Unspecified vulnerability in Citrix XenServer 5.0 Update 3 and earlier, and 5.5, allows local users to bypass authentication and execute unspecified Xen API (XAPI) calls via unknown vectors.

The physdevgetfreepirq hypercall in arch/x86/physdev.c in Xen 4.1.x and Citrix XenServer 6.0.2 and earlier uses the return value of the getfreepirq function as an array index without checking that the return value indicates an error, which allows guest OS users to cause a denial of service (invalid memory write and host crash) and possibly gain privileges via unspecified vectors.