CMPXCHG8B emulation in Xen 3.3.x through 4.7.x on x86 systems allows local HVM guest OS users to obtain sensitive information from host stack memory via a "supposedly-ignored" operand size prefix.

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

CVE-2016-9932 (XSA-200)

CMPXCHG8B emulation allows local HVM guest OS users to obtain sensitive information from host stack memory.

CVE-2017-7995

Description Xen checks access permissions to MMIO ranges only after accessing them, allowing host PCI device space memory reads.

CVE-2017-8903 (XSA-213)

Xen mishandles page tables after an IRET hypercall which can lead to arbitrary code execution on the host OS. The vulnerability is only exposed to 64-bit PV guests.

CVE-2017-8904 (XSA-214)

Xen mishandles the 'contains segment descriptors' property during GNTTABOP_transfer. This might allow PV guest OS users to execute arbitrary code on the host OS.

CVE-2017-8905 (XSA-215)

Xen mishandles a failsafe callback which might allow PV guest OS users to execute arbitrary code on the host OS.

For Debian 7 'Wheezy', these problems have been fixed in version 4.1.6.lts1-8.

We recommend that you upgrade your xen packages.

NOTE: Tenable Network Security has extracted the preceding description block directly from the DLA security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

Jan Beulich and Jann Horn discovered multiple vulnerabilities in the Xen hypervisor, which may lead to privilege escalation, guest-to-host breakout, denial of service or information leaks.

In additional to the CVE identifiers listed above, this update also addresses the vulnerabilities announced as XSA-213, XSA-214 and XSA-215.

This update for xen fixes several issues. These security issues were fixed :

  - CVE-2016-10155: The virtual hardware watchdog     'wdt_i6300esb' was vulnerable to a memory leakage issue     allowing a privileged user to cause a DoS and/or     potentially crash the Qemu process on the host     (bsc#1024183)

  - CVE-2017-2620: In CIRRUS_BLTMODE_MEMSYSSRC mode the     bitblit copy routine cirrus_bitblt_cputovideo failed to     check the memory region, allowing for an out-of-bounds     write that allows for privilege escalation (bsc#1024834)

  - CVE-2017-2615: An error in the bitblt copy operation     could have allowed a malicious guest administrator to     cause an out of bounds memory access, possibly leading     to information disclosure or privilege escalation     (bsc#1023004)

  - CVE-2014-8106: A heap-based buffer overflow in the     Cirrus VGA emulator allowed local guest users to execute     arbitrary code via vectors related to blit regions     (bsc#907805)

  - CVE-2016-9911: The USB EHCI Emulation support was     vulnerable to a memory leakage issue while processing     packet data in 'ehci_init_transfer'. A guest     user/process could have used this issue to leak host     memory, resulting in DoS for the host (bsc#1014507)

  - CVE-2016-9921: The Cirrus CLGD 54xx VGA Emulator support     was vulnerable to a divide by zero issue while copying     VGA data. A privileged user inside guest could have used     this flaw to crash the process instance on the host,     resulting in DoS (bsc#1015169)

  - CVE-2016-9922: The Cirrus CLGD 54xx VGA Emulator support     was vulnerable to a divide by zero issue while copying     VGA data. A privileged user inside guest could have used     this flaw to crash the process instance on the host,     resulting in DoS (bsc#1015169)

  - CVE-2016-10013: Xen allowed local 64-bit x86 HVM guest     OS users to gain privileges by leveraging mishandling of     SYSCALL singlestep during emulation (bsc#1016340).

  - CVE-2016-9932: CMPXCHG8B emulation on x86 systems     allowed local HVM guest OS users to obtain sensitive     information from host stack memory via a     'supposedly-ignored' operand size prefix (bsc#1012651).

  - CVE-2016-9101: A memory leak in hw/net/eepro100.c     allowed local guest OS administrators to cause a denial     of service (memory consumption and QEMU process crash)     by repeatedly unplugging an i8255x (PRO100) NIC device     (bsc#1013668)

  - CVE-2016-9776: The ColdFire Fast Ethernet Controller     emulator support was vulnerable to an infinite loop     issue while receiving packets in 'mcf_fec_receive'. A     privileged user/process inside guest could have used     this issue to crash the Qemu process on the host leading     to DoS (bsc#1013657)

  - A malicious guest could have, by frequently rebooting     over extended periods of time, run the host system out     of memory, resulting in a Denial of Service (DoS)     (bsc#1022871)

  - CVE-2016-10024: Xen allowed local x86 PV guest OS kernel     administrators to cause a denial of service (host hang     or crash) by modifying the instruction stream     asynchronously while performing certain kernel     operations (bsc#1014298)

The update package also includes non-security fixes. See advisory for details.

Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

According 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.

The version of Citrix XenServer installed on the remote host is missing a security hotfix. It is, therefore, affected by multiple vulnerabilities :

  - A flaw exists in x86 instruction CMPXCHG8B due to legacy     operand size overrides not being properly ignored when     handling prefixes. A guest attacker can exploit this to     disclose potentially sensitive information on the host     system. Note that the ability to read a small amount of     hypervisor memory is restricted to privileged-mode code     in all guests except on Citrix XenServer 6.2 SP1 and     6.0.2CC, where the attack may also be performed from     non-privileged-mode code in HVM guest VMs.
    (CVE-2016-9932)

  - A denial of service vulnerability exists when a guest     asynchronously modifies its instruction stream to effect     the clearing of EFLAGS.IF. A guest attacker can exploit     this to cause the host to hang or crash.
    (CVE-2016-10024)

  - A denial of service vulnerability exists due to a NULL     pointer dereference flaw that is triggered when the     hvmemul_vmfunc() function pointer uses inappropriate     NULL checks before indirect function calls. A guest     attacker can exploit this to cause the hypervisor to     crash. Note that the ability of privileged-mode code in     HVM guest VMs to crash the host is restricted to AMD     systems running Citrix XenServer 7.0. (CVE-2016-10025)

This updates xen to version 4.4.4_06 to fix the following issues :

  - An unprivileged user in a guest could gain guest could     escalate privilege to that of the guest kernel, if it     had could invoke the instruction emulator. Only 64-bit     x86 HVM guest were affected. Linux guest have not been     vulnerable. (boo#1016340, CVE-2016-10013)

  - An unprivileged user in a 64 bit x86 guest could gain     information from the host, crash the host or gain     privilege of the host (boo#1009107, CVE-2016-9383)

  - An unprivileged guest process could (unintentionally or     maliciously) obtain or ocorrupt sensitive information of     other programs in the same guest. Only x86 HVM guests     have been affected. The attacker needs to be able to     trigger the Xen instruction emulator. (boo#1000106,     CVE-2016-7777)

  - A guest on x86 systems could read small parts of     hypervisor stack data (boo#1012651, CVE-2016-9932)

  - A malicious guest kernel could hang or crash the host     system (boo#1014298, CVE-2016-10024)

  - A malicious guest administrator could escalate their     privilege to that of the host. Only affects x86 HVM     guests using qemu older version 1.6.0 or using the     qemu-xen-traditional. (boo#1011652, CVE-2016-9637)

  - An unprivileged guest user could escalate privilege to     that of the guest administrator on x86 HVM guests,     especially on Intel CPUs (boo#1009100, CVE-2016-9386)

  - An unprivileged guest user could escalate privilege to     that of the guest administrator (on AMD CPUs) or crash     the system (on Intel CPUs) on 32-bit x86 HVM guests.
    Only guest operating systems that allowed a new task to     start in VM86 mode were affected. (boo#1009103,     CVE-2016-9382)

  - A malicious guest administrator could crash the host on     x86 PV guests only (boo#1009104, CVE-2016-9385)

  - A malicious guest administrator could get privilege of     the host emulator process on x86 HVM guests.
    (boo#1009109, CVE-2016-9381)

  - A vulnerability in pygrub allowed a malicious guest     administrator to obtain the contents of sensitive host     files, or even delete those files (boo#1009111,     CVE-2016-9379, CVE-2016-9380)

  - A privileged guest user could cause an infinite loop in     the RTL8139 ethernet emulation to consume CPU cycles on     the host, causing a DoS situation (boo#1007157,     CVE-2016-8910)

  - A privileged guest user could cause an infinite loop in     the intel-hda sound emulation to consume CPU cycles on     the host, causing a DoS situation (boo#1007160,     CVE-2016-8909)

  - A privileged guest user could cause a crash of the     emulator process on the host by exploiting a divide by     zero vulnerability of the JAZZ RC4030 chipset emulation     (boo#1005004 CVE-2016-8667)

  - A privileged guest user could cause a crash of the     emulator process on the host by exploiting a divide by     zero issue of the 16550A UART emulation (boo#1005005,     CVE-2016-8669)

  - A privileged guest user could cause an infinite loop in     the USB xHCI emulation, causing a DoS situation on the     host (boo#1004016, CVE-2016-8576)

  - A privileged guest user could cause an infinite loop in     the ColdFire Fash Ethernet Controller emulation, causing     a DoS situation on the host (boo#1003030, CVE-2016-7908)

  - A privileged guest user could cause an infinite loop in     the AMD PC-Net II emulation, causing a DoS situation on     the host (boo#1003032, CVE-2016-7909)

  - Cause a reload of clvm in the block-dmmd script to avoid     a blocking lvchange call (boo#1002496)

  - Also unplug SCSI disks in qemu-xen-traditional for     upstream unplug protocol. Before a single SCSI storage     devices added to HVM guests could appear multiple times     in the guest. (boo#953518)

  - Fix a kernel panic / black screen when trying to boot a     XEN kernel on some UEFI firmwares (boo#1000195)

This updates xen to version 4.5.5 to fix the following issues :

  - An unprivileged user in a guest could gain guest could     escalate privilege to that of the guest kernel, if it     had could invoke the instruction emulator. Only 64-bit     x86 HVM guest were affected. Linux guest have not been     vulnerable. (boo#1016340, CVE-2016-10013)

  - An unprivileged user in a 64 bit x86 guest could gain     information from the host, crash the host or gain     privilege of the host (boo#1009107, CVE-2016-9383)

  - An unprivileged guest process could (unintentionally or     maliciously) obtain or ocorrupt sensitive information of     other programs in the same guest. Only x86 HVM guests     have been affected. The attacker needs to be able to     trigger the Xen instruction emulator. (boo#1000106,     CVE-2016-7777)

  - A guest on x86 systems could read small parts of     hypervisor stack data (boo#1012651, CVE-2016-9932)

  - A malicious guest kernel could hang or crash the host     system (boo#1014298, CVE-2016-10024)

  - The epro100 emulated network device caused a memory leak     in the host when unplugged in the guest. A privileged     user in the guest could use this to cause a DoS on the     host or potentially crash the guest process on the host     (boo#1013668, CVE-2016-9101)

  - The ColdFire Fast Ethernet Controller was vulnerable to     an infinite loop that could be trigged by a privileged     user in the guest, leading to DoS (boo#1013657,     CVE-2016-9776)

  - A malicious guest administrator could escalate their     privilege to that of the host. Only affects x86 HVM     guests using qemu older version 1.6.0 or using the     qemu-xen-traditional. (boo#1011652, CVE-2016-9637)

  - An unprivileged guest user could escalate privilege to     that of the guest administrator on x86 HVM guests,     especially on Intel CPUs (boo#1009100, CVE-2016-9386)

  - An unprivileged guest user could escalate privilege to     that of the guest administrator (on AMD CPUs) or crash     the system (on Intel CPUs) on 32-bit x86 HVM guests.
    Only guest operating systems that allowed a new task to     start in VM86 mode were affected. (boo#1009103,     CVE-2016-9382)

  - A malicious guest administrator could crash the host on     x86 PV guests only (boo#1009104, CVE-2016-9385)

  - An unprivileged guest user was able to crash the guest.
    (boo#1009108, CVE-2016-9377, CVE-2016-9378)

  - A malicious guest administrator could get privilege of     the host emulator process on x86 HVM guests.
    (boo#1009109, CVE-2016-9381)

  - A vulnerability in pygrub allowed a malicious guest     administrator to obtain the contents of sensitive host     files, or even delete those files (boo#1009111,     CVE-2016-9379, CVE-2016-9380)

  - A privileged guest user could cause an infinite loop in     the RTL8139 ethernet emulation to consume CPU cycles on     the host, causing a DoS situation (boo#1007157,     CVE-2016-8910)

  - A privileged guest user could cause an infinite loop in     the intel-hda sound emulation to consume CPU cycles on     the host, causing a DoS situation (boo#1007160,     CVE-2016-8909)

  - A privileged guest user could cause a crash of the     emulator process on the host by exploiting a divide by     zero vulnerability of the JAZZ RC4030 chipset emulation     (boo#1005004 CVE-2016-8667)

  - A privileged guest user could cause a crash of the     emulator process on the host by exploiting a divide by     zero issue of the 16550A UART emulation (boo#1005005,     CVE-2016-8669)

  - A privileged guest user could cause a memory leak in the     USB EHCI emulation, causing a DoS situation on the host     (boo#1003870, CVE-2016-7995)

  - A privileged guest user could cause an infinite loop in     the USB xHCI emulation, causing a DoS situation on the     host (boo#1004016, CVE-2016-8576)

  - A privileged guest user could cause an infinite loop in     the ColdFire Fash Ethernet Controller emulation, causing     a DoS situation on the host (boo#1003030, CVE-2016-7908)

  - A privileged guest user could cause an infinite loop in     the AMD PC-Net II emulation, causing a DoS situation on     the host (boo#1003032, CVE-2016-7909)

  - Cause a reload of clvm in the block-dmmd script to avoid     a blocking lvchange call (boo#1002496)

This update for xen fixes the following issues :

  - A Mishandling of SYSCALL singlestep during emulation     which could have lead to privilege escalation. (XSA-204,     bsc#1016340, CVE-2016-10013)

  - CMPXCHG8B emulation failed to ignore operand size     override which could have lead to information     disclosure. (XSA-200, bsc#1012651, CVE-2016-9932)

  - PV guests may have been able to mask interrupts causing     a Denial of Service. (XSA-202, bsc#1014298,     CVE-2016-10024)

  - A missing NULL pointer check in VMFUNC emulation could     lead to a hypervisor crash leading to a Denial of     Servce. (XSA-203, bsc#1014300, CVE-2016-10025)

This update was imported from the SUSE:SLE-12-SP2:Update update project.

The remote host is affected by the vulnerability described in GLSA-201612-56 (Xen: Multiple vulnerabilities)

    Multiple vulnerabilities have been discovered in Xen. Please review the       CVE identifiers referenced below for details.
  Impact :

    A local attacker could possibly execute arbitrary code with the       privileges of the process, could gain privileges on the host system,       cause a Denial of Service condition, or obtain sensitive information.
  Workaround :

    There is no known workaround at this time.

x86 CMPXCHG8B emulation fails to ignore operand size override [XSA-200, CVE-2016-9932] (#1404262)

----

ARM guests may induce host asynchronous abort [XSA-201, CVE-2016-9815, CVE-2016-9816, CVE-2016-9817, CVE-2016-9818] (#1399747) qemu: Divide by zero vulnerability in cirrus_do_copy (#1399055) [CVE-2016-9921, CVE-2016-9922] Qemu: 9pfs: memory leakage via proxy/handle callbacks (#1402278) qemu ioport array overflow [XSA-199, CVE-2016-9637]

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora update system website.
Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

This update for xen fixes the following issues :

  - A Mishandling of SYSCALL singlestep during emulation     which could have lead to privilege escalation. (XSA-204,     bsc#1016340, CVE-2016-10013)

  - CMPXCHG8B emulation failed to ignore operand size     override which could have lead to information     disclosure. (XSA-200, bsc#1012651, CVE-2016-9932)

  - PV guests may have been able to mask interrupts causing     a Denial of Service. (XSA-202, bsc#1014298,     CVE-2016-10024)

Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

This update for xen fixes the following issues :

  - A Mishandling of SYSCALL singlestep during emulation     which could have lead to privilege escalation. (XSA-204,     bsc#1016340, CVE-2016-10013)

  - CMPXCHG8B emulation failed to ignore operand size     override which could have lead to information     disclosure. (XSA-200, bsc#1012651, CVE-2016-9932)

  - PV guests may have been able to mask interrupts causing     a Denial of Service. (XSA-202, bsc#1014298,     CVE-2016-10024)

  - A missing NULL pointer check in VMFUNC emulation could     lead to a hypervisor crash leading to a Denial of     Servce. (XSA-203, bsc#1014300, CVE-2016-10025)

Note that Tenable Network Security has extracted the preceding description block directly from the SUSE security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

x86 CMPXCHG8B emulation fails to ignore operand size override [XSA-200, CVE-2016-9932] (#1404262)

----

ARM guests may induce host asynchronous abort [XSA-201, CVE-2016-9815,

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora update system website.
Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

The Xen Project reports :

The x86 instruction CMPXCHG8B is supposed to ignore legacy operand size overrides; it only honors the REX.W override (making it CMPXCHG16B). So, the operand size is always 8 or 16. When support for CMPXCHG16B emulation was added to the instruction emulator, this restriction on the set of possible operand sizes was relied on in some parts of the emulation; but a wrong, fully general, operand size value was used for other parts of the emulation. As a result, if a guest uses a supposedly-ignored operand size prefix, a small amount of hypervisor stack data is leaked to the guests: a 96 bit leak to guests running in 64-bit mode; or, a 32 bit leak to other guests.

A malicious unprivileged guest may be able to obtain sensitive information from the host.

ID	Name	Product	Family	Severity
100575	Debian DLA-964-1 : xen security update	Nessus	Debian Local Security Checks	high
100071	Debian DSA-3847-1 : xen - security update	Nessus	Debian Local Security Checks	high
97828	SUSE SLES11 Security Update : xen (SUSE-SU-2017:0718-1)	Nessus	SuSE Local Security Checks	critical
96957	Xen CMPXCHG8B Emulation Information Disclosure (XSA-200)	Nessus	Misc.	low
96778	Citrix XenServer Multiple Vulnerabilities (CTX219378)	Nessus	Misc.	low
96253	openSUSE Security Update : xen (openSUSE-2017-5)	Nessus	SuSE Local Security Checks	high
96252	openSUSE Security Update : xen (openSUSE-2017-4)	Nessus	SuSE Local Security Checks	high
96250	openSUSE Security Update : xen (openSUSE-2017-2)	Nessus	SuSE Local Security Checks	high
96231	GLSA-201612-56 : Xen: Multiple vulnerabilities	Nessus	Gentoo Local Security Checks	high
96113	Fedora 24 : xen (2016-bcbae0781f)	Nessus	Fedora Local Security Checks	high
96087	SUSE SLES12 Security Update : xen (SUSE-SU-2016:3241-1)	Nessus	SuSE Local Security Checks	high
96081	SUSE SLES11 Security Update : xen (SUSE-SU-2016:3221-1)	Nessus	SuSE Local Security Checks	high
96076	SUSE SLED12 / SLES12 Security Update : xen (SUSE-SU-2016:3208-1)	Nessus	SuSE Local Security Checks	high
96075	SUSE SLED12 / SLES12 Security Update : xen (SUSE-SU-2016:3207-1)	Nessus	SuSE Local Security Checks	high
95945	Fedora 25 : xen (2016-1b868c23a9)	Nessus	Fedora Local Security Checks	medium
95787	FreeBSD : xen-kernel -- x86 CMPXCHG8B emulation fails to ignore operand size override (80a897a2-c1a6-11e6-ae1b-002590263bf5)	Nessus	FreeBSD Local Security Checks	low

Detections

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CVE-2016-9932

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Tenable Plugins

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critical

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