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AUSCERT External Security Bulletin Redistribution
Xen Security Advisory XSA-132
29 April 2015
AusCERT Security Bulletin Summary
Operating System: Xen
Impact/Access: Access Confidential Data -- Existing Account
CVE Names: CVE-2015-3340
Revision History: April 29 2015: CVE assigned
April 22 2015: Initial Release
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Xen Security Advisory CVE-2015-3340 / XSA-132
Information leak through XEN_DOMCTL_gettscinfo
UPDATES IN VERSION 2
The handler for XEN_DOMCTL_gettscinfo failed to initialize a padding
field subsequently copied to guest memory.
A similar leak existed in XEN_SYSCTL_getdomaininfolist, which is being
addressed here regardless of that operation being declared unsafe for
disaggregation by XSA-77.
Malicious or buggy stub domain kernels or tool stacks otherwise living
outside of Domain0 may be able to read sensitive data relating to the
hypervisor or other guests not under the control of that domain.
Xen 4.0.x and later are vulnerable.
Only x86 systems are vulnerable. ARM systems are not vulnerable.
The vulnerability is only exposed to service domains with privilege over
another guest. In a usual configuration that means only device model
emulators (qemu-dm) when these are running in a separate domain.
In the case of HVM guests whose device model is running in an
unrestricted dom0 process, qemu-dm already has the ability to cause
problems for the whole system. So in that case the vulnerability is
This vulnerability is applicable for an HVM guest with a stub qemu-dm.
That is, where the device model runs in a separate domain (in the case
of xl, as requested by "device_model_stubdomain_override=1" in the xl
domain configuration file). In this case a guest which has already
exploited another vulnerability, to gain control of the device model,
would be able to exercise the information leak.
However, the security of a system with qemu-dm running in a stub domain
is still better than with a qemu-dm running as an unrestricted dom0
process. Therefore users with these configurations should not switch
to an unrestricted dom0 qemu-dm.
Finally, in a radically disaggregated system, where the service domain
software (probably, the device model domain image in the HVM case) is
not always supplied by the host administrator, a malicious service
domain administrator can exercise this vulnerability.
There is no mitigation available.
In a radically disaggregated system, restricting HVM service domains
to software images approved by the host administrator will avoid the
vulnerability (so long as there isn't also a vulnerability in the
NOTE REGARDING LACK OF EMBARGO
The fix for this bug was publicly posted on xen-devel, before it was
appreciated that there was a security problem.
This issue was recognized as security issue by Jan Beulich of SUSE.
Applying the appropriate attached patch resolves this issue.
xsa132-unstable.patch xen-unstable, Xen 4.5.x, Xen 4.4.x, Xen 4.3.x
xsa132-4.2.patch Xen 4.2.x
$ sha256sum xsa132*.patch
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