It was found that the Xen hypervisor x86 CPU emulator implementation did not correctly handle certain instructions with segment overrides, potentially resulting in a memory corruption. A malicious guest user could use this flaw to read arbitrary data relating to other guests, cause a denial of service on the host, or potentially escalate their privileges on the host.
Instructions with register operands ignore eventual segment overrides
encoded for them. Due to an insufficiently conditional assignment such
a bogus segment override can, however, corrupt a pointer used
subsequently to store the result of the instruction.
A malicious guest might be able to read sensitive data relating to
other guests, or to cause denial of service on the host. Arbitrary code
execution, and therefore privilege escalation, cannot be excluded.
Xen 3.2.x and later are vulnerable.
Xen 3.1.x and earlier have not been inspected.
Only x86 systems are vulnerable. ARM systems are not vulnerable.
There is no mitigation available for this issue.
Applying the appropriate attached patch resolves this issue.
xsa123.patch xen-unstable, Xen 4.5.x, Xen 4.4.x
xsa123-4.3-4.2.patch Xen 4.3.x, Xen 4.2.x
$ sha256sum xsa123*.patch
Created attachment 995257 [details]
Created attachment 995258 [details]
This issue does affect the Xen hypervisor packages as shipped with Red Hat Enterprise Linux 5. Future Xen hypervisor packages updates might address this issue.
Created xen tracking bugs for this issue:
Affects: fedora-all [bug 1200398]
xen-4.5.0-6.fc22 has been pushed to the Fedora 22 stable repository. If problems still persist, please make note of it in this bug report.
xen-4.3.3-12.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.
xen-4.4.1-16.fc21 has been pushed to the Fedora 21 stable repository. If problems still persist, please make note of it in this bug report.
This issue has been addressed in the following products:
Red Hat Enterprise Linux 5
Via RHSA-2016:0450 https://rhn.redhat.com/errata/RHSA-2016-0450.html