xen : various security flaws (#1397383) x86 null segments not always treated as unusable [XSA-191, CVE-2016-9386] x86 task switch to VM86 mode mis-handled [XSA-192, CVE-2016-9382] x86 segment base write emulation lacking canonical address checks [XSA-193, CVE-2016-9385] guest 32-bit ELF symbol table load leaking host data [XSA-194, CVE-2016-9384] x86 64-bit bit test instruction emulation broken [XSA-195, CVE-2016-9383] x86 software interrupt injection mis-handled [XSA-196, CVE-2016-9377, CVE-2016-9378] qemu incautious about shared ring processing [XSA-197, CVE-2016-9381] delimiter injection vulnerabilities in pygrub [XSA-198, CVE-2016-9379, CVE-2016-9380]

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 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.

The Xen Project reports :

Along with their main kernel binary, unprivileged guests may arrange to have their Xen environment load (kernel) symbol tables for their use. The ELF image metadata created for this purpose has a few unused bytes when the symbol table binary is in 32-bit ELF format. These unused bytes were not properly cleared during symbol table loading.

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

The information leak is small and not under the control of the guest, so effectively exploiting this vulnerability is probably difficult.

xen was updated to version 4.7.1 to fix 17 security issues.

These security issues were fixed :

  - CVE-2016-9637: ioport array overflow allowing a     malicious guest administrator can escalate their     privilege to that of the host (bsc#1011652).

  - CVE-2016-9386: x86 null segments were not always treated     as unusable allowing an unprivileged guest user program     to elevate its privilege to that of the guest operating     system. Exploit of this vulnerability is easy on Intel     and more complicated on AMD (bsc#1009100).

  - CVE-2016-9382: x86 task switch to VM86 mode was     mis-handled, allowing a unprivileged guest process to     escalate its privilege to that of the guest operating     system on AMD hardware. On Intel hardware a malicious     unprivileged guest process can crash the guest     (bsc#1009103).

  - CVE-2016-9385: x86 segment base write emulation lacked     canonical address checks, allowing a malicious guest     administrator to crash the host (bsc#1009104).

  - CVE-2016-9384: Guest 32-bit ELF symbol table load     leaking host data to unprivileged guest users     (bsc#1009105).

  - CVE-2016-9383: The x86 64-bit bit test instruction     emulation was broken, allowing a guest to modify     arbitrary memory leading to arbitray code execution     (bsc#1009107).

  - CVE-2016-9377: x86 software interrupt injection was     mis-handled, allowing an unprivileged guest user to     crash the guest (bsc#1009108).

  - CVE-2016-9378: x86 software interrupt injection was     mis-handled, allowing an unprivileged guest user to     crash the guest (bsc#1009108)

  - CVE-2016-9381: Improper processing of shared rings     allowing guest administrators take over the qemu     process, elevating their privilege to that of the qemu     process (bsc#1009109).

  - CVE-2016-9379: Delimiter injection vulnerabilities in     pygrub allowed guest administrators to obtain the     contents of sensitive host files or delete the files     (bsc#1009111).

  - CVE-2016-9380: Delimiter injection vulnerabilities in     pygrub allowed guest administrators to obtain the     contents of sensitive host files or delete the files     (bsc#1009111).

  - CVE-2016-7777: Xen did not properly honor CR0.TS and     CR0.EM, which allowed local x86 HVM guest OS 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 (bsc#1000106).

  - CVE-2016-8910: The rtl8139_cplus_transmit function in     hw/net/rtl8139.c allowed local guest OS administrators     to cause a denial of service (infinite loop and CPU     consumption) by leveraging failure to limit the ring     descriptor count (bsc#1007157).

  - CVE-2016-8667: The rc4030_write function in     hw/dma/rc4030.c in allowed local guest OS administrators     to cause a denial of service (divide-by-zero error and     QEMU process crash) via a large interval timer reload     value (bsc#1005004).

  - CVE-2016-8669: The serial_update_parameters function in     hw/char/serial.c allowed local guest OS administrators     to cause a denial of service (divide-by-zero error and     QEMU process crash) via vectors involving a value of     divider greater than baud base (bsc#1005005).

  - CVE-2016-7908: The mcf_fec_do_tx function in     hw/net/mcf_fec.c did not properly limit the buffer     descriptor count when transmitting packets, which     allowed local guest OS administrators to cause a denial     of service (infinite loop and QEMU process crash) via     vectors involving a buffer descriptor with a length of 0     and crafted values in bd.flags (bsc#1003030).

  - CVE-2016-7909: The pcnet_rdra_addr function in     hw/net/pcnet.c allowed local guest OS administrators to     cause a denial of service (infinite loop and QEMU     process crash) by setting the (1) receive or (2)     transmit descriptor ring length to 0 (bsc#1003032).

These non-security issues were fixed :

  - bsc#1004981: Xen RPM didn't contain debug hypervisor for     EFI systems

  - bsc#1007941: Xen tools limited the number of vcpus to     256 

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

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 multiple vulnerabilities :

  - A flaw exists in the inject_swint() function in     x86_emulate.c due to improper handling of the format of     IDT lookups when emulating instructions which generate     software interrupts. A guest attacker can exploit this     to crash the host, resulting in a denial of service     condition. (CVE-2016-9377)

  - A flaw exists in the svm_inject_trap() function in svm.c     due to a failure to properly perform IDT privilege     checks when emulating instructions which generate     software interrupts. A guest attacker can exploit this     to crash the host, resulting in a denial of service     condition. (CVE-2016-9378)

  - A flaw exists in the sniff_netware() function in file     tools/pygrub/src/pygrub due to improper handling of     string quotes and S-expressions in the bootloader when     the S-expressions output format is requested. A guest     attacker can exploit this to cause the bootloader     configuration file to produce incorrect output,     resulting in the disclosure or deletion of files from     the host. (CVE-2016-9379)

  - A flaw exists in the sniff_netware() function in file     tools/pygrub/src/pygrub due to improper handling of NULL     bytes in the bootloader when the null-delimited output     format is requested. A guest attacker can exploit this     to cause configuration files to output ambiguous or     confusing results, resulting in the disclosure or     deletion of files from the host. (CVE-2016-9380)

  - A double-fetch flaw exists that is triggered when the     compiler omits QEMU optimizations. A guest attacker can     exploit this to gain elevated privileges on the host.
    (CVE-2016-9381)

  - A flaw exists in the hvm_task_switch() function in hvm.c     due to improper handling of x86 task switching to VM86     mode. A guest attacker can exploit this to cause a     denial of service condition or gain elevated privileges     within the guest environment. (CVE-2016-9382)

  - A flaw exists in the x86_emulate() function in     x86_emulate.c that allows a guest attacker to cause     changes to memory and thereby gain elevated privileges     on the host. (CVE-2016-9383)

  - A flaw exists that is triggered as unused bytes in     image metadata are not properly cleared during symbol     table loading. This may allow a guest attacker to     disclose potentially sensitive information from the     host. (CVE-2016-9384)

  - A flaw exists due to improper clearing of unused bytes     in image metadata during symbol table loading. A guest     attacker can exploit this to disclose sensitive     information from the host. (CVE-2016-9384)

  - A flaw exists in the x86 segment base write emulation     due to a lack of canonical address checks. A guest     attacker can exploit this issue to crash the host,     resulting in a denial of service condition.
    (CVE-2016-9385)

  - A flaw exists in the x86 emulator due to improper     validation of the usability of segments when performing     memory accesses. A guest attacker can exploit this to     gain elevated privileges within the guest environment.
    (CVE-2016-9386)

Note that Nessus has checked 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.

xen was updated to version 4.7.1 to fix 17 security issues. These security issues were fixed :

  - CVE-2016-9637: ioport array overflow allowing a     malicious guest administrator can escalate their     privilege to that of the host (bsc#1011652).

  - CVE-2016-9386: x86 null segments were not always treated     as unusable allowing an unprivileged guest user program     to elevate its privilege to that of the guest operating     system. Exploit of this vulnerability is easy on Intel     and more complicated on AMD (bsc#1009100).

  - CVE-2016-9382: x86 task switch to VM86 mode was     mis-handled, allowing a unprivileged guest process to     escalate its privilege to that of the guest operating     system on AMD hardware. On Intel hardware a malicious     unprivileged guest process can crash the guest     (bsc#1009103).

  - CVE-2016-9385: x86 segment base write emulation lacked     canonical address checks, allowing a malicious guest     administrator to crash the host (bsc#1009104).

  - CVE-2016-9384: Guest 32-bit ELF symbol table load     leaking host data to unprivileged guest users     (bsc#1009105).

  - CVE-2016-9383: The x86 64-bit bit test instruction     emulation was broken, allowing a guest to modify     arbitrary memory leading to arbitray code execution     (bsc#1009107).

  - CVE-2016-9377: x86 software interrupt injection was     mis-handled, allowing an unprivileged guest user to     crash the guest (bsc#1009108).

  - CVE-2016-9378: x86 software interrupt injection was     mis-handled, allowing an unprivileged guest user to     crash the guest (bsc#1009108)

  - CVE-2016-9381: Improper processing of shared rings     allowing guest administrators take over the qemu     process, elevating their privilege to that of the qemu     process (bsc#1009109).

  - CVE-2016-9379: Delimiter injection vulnerabilities in     pygrub allowed guest administrators to obtain the     contents of sensitive host files or delete the files     (bsc#1009111).

  - CVE-2016-9380: Delimiter injection vulnerabilities in     pygrub allowed guest administrators to obtain the     contents of sensitive host files or delete the files     (bsc#1009111).

  - CVE-2016-7777: Xen did not properly honor CR0.TS and     CR0.EM, which allowed local x86 HVM guest OS 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 (bsc#1000106).

  - CVE-2016-8910: The rtl8139_cplus_transmit function in     hw/net/rtl8139.c allowed local guest OS administrators     to cause a denial of service (infinite loop and CPU     consumption) by leveraging failure to limit the ring     descriptor count (bsc#1007157).

  - CVE-2016-8667: The rc4030_write function in     hw/dma/rc4030.c in allowed local guest OS administrators     to cause a denial of service (divide-by-zero error and     QEMU process crash) via a large interval timer reload     value (bsc#1005004).

  - CVE-2016-8669: The serial_update_parameters function in     hw/char/serial.c allowed local guest OS administrators     to cause a denial of service (divide-by-zero error and     QEMU process crash) via vectors involving a value of     divider greater than baud base (bsc#1005005).

  - CVE-2016-7908: The mcf_fec_do_tx function in     hw/net/mcf_fec.c did not properly limit the buffer     descriptor count when transmitting packets, which     allowed local guest OS administrators to cause a denial     of service (infinite loop and QEMU process crash) via     vectors involving a buffer descriptor with a length of 0     and crafted values in bd.flags (bsc#1003030).

  - CVE-2016-7909: The pcnet_rdra_addr function in     hw/net/pcnet.c allowed local guest OS administrators to     cause a denial of service (infinite loop and QEMU     process crash) by setting the (1) receive or (2)     transmit descriptor ring length to 0 (bsc#1003032).

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.

ID	Name	Product	Family	Published	Updated	Severity
95493	Fedora 25 : xen (2016-999e1a6927)	Nessus	Fedora Local Security Checks	12/5/2016	1/11/2021	high
96231	GLSA-201612-56 : Xen: Multiple vulnerabilities	Nessus	Gentoo Local Security Checks	1/3/2017	1/11/2021	high
95508	FreeBSD : xen-kernel -- guest 32-bit ELF symbol table load leaking host data (5555120d-ba4d-11e6-ae1b-002590263bf5)	Nessus	FreeBSD Local Security Checks	12/5/2016	1/4/2021	medium
95910	openSUSE Security Update : xen (openSUSE-2016-1477)	Nessus	SuSE Local Security Checks	12/16/2016	1/19/2021	high
95630	Xen Multiple Vulnerabilities (XSA-191 - XSA-198)	Nessus	Misc.	12/8/2016	7/10/2020	high
95709	SUSE SLED12 / SLES12 Security Update : xen (SUSE-SU-2016:3067-1)	Nessus	SuSE Local Security Checks	12/12/2016	1/6/2021	high

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