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Debian Security Advisory DSA-3729-1                   security@debian.org
https://www.debian.org/security/                     Salvatore Bonaccorso
December 07, 2016                     https://www.debian.org/security/faq
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Package        : xen
CVE ID         : CVE-2016-7777 CVE-2016-9379 CVE-2016-9380 CVE-2016-9382
                 CVE-2016-9383 CVE-2016-9385 CVE-2016-9386
Debian Bug     : 845663 845664 845665 845668 845670

Multiple vulnerabilities have been discovered in the Xen hypervisor. The
Common Vulnerabilities and Exposures project identifies the following
problems:

CVE-2016-7777 (XSA-190)

    Jan Beulich from SUSE discovered that Xen does not properly honor
    CR0.TS and CR0.EM for x86 HVM guests, potentially allowing guest
    users to read or modify FPU, MMX, or XMM register state information
    belonging to arbitrary tasks on the guest by modifying an
    instruction while the hypervisor is preparing to emulate it.

CVE-2016-9379, CVE-2016-9380 (XSA-198)

    Daniel Richman and Gabor Szarka of the Cambridge University
    Student-Run Computing Facility discovered that pygrub, the boot
    loader emulator, fails to quote (or sanity check) its results when
    reporting them to its caller. A malicious guest administrator can
    take advantage of this flaw to cause an information leak or denial
    of service.

CVE-2016-9382 (XSA-192)

    Jan Beulich of SUSE discovered that Xen does not properly handle x86
    task switches to VM86 mode. A unprivileged guest process can take
    advantage of this flaw to crash the guest or, escalate its
    privileges to that of the guest operating system.

CVE-2016-9383 (XSA-195)

    George Dunlap of Citrix discovered that the Xen x86 64-bit bit test
    instruction emulation is broken. A malicious guest can take
    advantage of this flaw to modify arbitrary memory, allowing for
    arbitrary code execution, denial of service (host crash), or
    information leaks.

CVE-2016-9385 (XSA-193)

    Andrew Cooper of Citrix discovered that Xen's x86 segment base write
    emulation lacks canonical address checks. A malicious guest
    administrator can take advantage of this flaw to crash the host,
    leading to a denial of service.

CVE-2016-9386 (XSA-191)

    Andrew Cooper of Citrix discovered that x86 null segments are not
    always treated as unusable. An unprivileged guest user program
    may be able to elevate its privilege to that of the guest
    operating system.

For the stable distribution (jessie), these problems have been fixed in
version 4.4.1-9+deb8u8.

We recommend that you upgrade your xen packages.

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