Xen CMPXCHG8B Emulation Information Disclosure (XSA-200)
Low Nessus Plugin ID 96957
SynopsisThe remote Xen hypervisor installation is missing a security update.
DescriptionAccording to its self-reported version number, the Xen hypervisor installed on the remote host is missing a security update. It is, therefore, affected by an information disclosure vulnerability due to a flaw in the x86 instruction CMPXCHG8B when handling prefixes. This is triggered because legacy operand size overrides are not properly ignored. A guest attacker can exploit this issue to disclose potentially sensitive information from the hypervisor stack of the host system.
Please note the following items :
- Only x86 systems are affected. ARM systems are not affected.
- On Xen version 4.6 and earlier, the vulnerability is exposed to all HVM guest user processes, including unprivileged processes.
- On Xen version 4.7, the vulnerability is exposed only to HVM guest user processes granted a degree of privilege (e.g., direct hardware access) by the guest administrator, or else to all user processes when the VM has been explicitly configured with a non-default CPU vendor string (in xm/xl, this would be done with a 'cpuid=' domain config option).
Note that Nessus has not tested for this vulnerability but has instead relied only on the changeset versions based on the xen.git change log.
Nessus did not check guest hardware configurations or if patches were applied manually to the source code before a recompile and reinstall.
SolutionApply the appropriate patch according to the vendor advisory.