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Debian Security Advisory DSA-4112-1                   security@debian.org
https://www.debian.org/security/                       Moritz Muehlenhoff
February 14, 2018                     https://www.debian.org/security/faq
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Package        : xen
CVE ID         : CVE-2017-17563 CVE-2017-17564 CVE-2017-17565
                 CVE-2017-17566

Multiple vulnerabilities have been discovered in the Xen hypervisor:

CVE-2017-17563

    Jan Beulich discovered that an incorrect reference count overflow
    check in x86 shadow mode may result in denial of service or
    privilege escalation.

CVE-2017-17564

    Jan Beulich discovered that improper x86 shadow mode reference count
    error handling may result in denial of service or privilege
    escalation.

CVE-2017-17565

    Jan Beulich discovered that an incomplete bug check in x86 log-dirty
    handling may result in denial of service.

CVE-2017-17566

    Jan Beulich discovered that x86 PV guests may gain access to
    internally used pages which could result in denial of service or
    potential privilege escalation.

In addition this update ships the "Comet" shim to address the Meltdown
class of vulnerabilities for guests with legacy PV kernels. In addition,
the package provides the "Xen PTI stage 1" mitigation which is built-in
and enabled by default on Intel systems, but can be disabled with
`xpti=false' on the hypervisor command line (It does not make sense to
use both xpti and the Comet shim.)

Please refer to the following URL for more details on how to configure
individual mitigation strategies:
https://xenbits.xen.org/xsa/advisory-254.html

Additional information can also be found in README.pti and README.comet.

For the stable distribution (stretch), these problems have been fixed in
version 4.8.3+comet2+shim4.10.0+comet3-1+deb9u4.1.

We recommend that you upgrade your xen packages.

For the detailed security status of xen please refer to
its security tracker page at:
https://security-tracker.debian.org/tracker/xen

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://www.debian.org/security/

Mailing list: debian-security-announce@lists.debian.org
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