Ubuntu 20.04 LTS : Linux kernel vulnerabilities (USN-4751-1)

##
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Ubuntu Security Notice USN-4751-1. The text
# itself is copyright (C) Canonical, Inc. See
# <https://ubuntu.com/security/notices>. Ubuntu(R) is a registered
# trademark of Canonical, Inc.
##

include('compat.inc');

if (description)
{
  script_id(147978);
  script_version("1.8");
  script_set_attribute(attribute:"plugin_modification_date", value:"2024/01/09");

  script_cve_id(
    "CVE-2020-25656",
    "CVE-2020-25668",
    "CVE-2020-25669",
    "CVE-2020-25704",
    "CVE-2020-27673",
    "CVE-2020-27675",
    "CVE-2020-27777",
    "CVE-2020-27815",
    "CVE-2020-27830",
    "CVE-2020-27835",
    "CVE-2020-28588",
    "CVE-2020-28941",
    "CVE-2020-28974",
    "CVE-2020-29568",
    "CVE-2020-29569",
    "CVE-2020-29660",
    "CVE-2020-29661",
    "CVE-2020-35508"
  );
  script_xref(name:"USN", value:"4751-1");

  script_name(english:"Ubuntu 20.04 LTS : Linux kernel vulnerabilities (USN-4751-1)");

  script_set_attribute(attribute:"synopsis", value:
"The remote Ubuntu host is missing one or more security updates.");
  script_set_attribute(attribute:"description", value:
"The remote Ubuntu 20.04 LTS host has a package installed that is affected by multiple vulnerabilities as referenced in
the USN-4751-1 advisory.

  - A flaw was found in the Linux kernel. A use-after-free was found in the way the console subsystem was
    using ioctls KDGKBSENT and KDSKBSENT. A local user could use this flaw to get read memory access out of
    bounds. The highest threat from this vulnerability is to data confidentiality. (CVE-2020-25656)

  - A flaw was found in Linux Kernel because access to the global variable fg_console is not properly
    synchronized leading to a use after free in con_font_op. (CVE-2020-25668)

  - A vulnerability was found in the Linux Kernel where the function sunkbd_reinit having been scheduled by
    sunkbd_interrupt before sunkbd being freed. Though the dangling pointer is set to NULL in
    sunkbd_disconnect, there is still an alias in sunkbd_reinit causing Use After Free. (CVE-2020-25669)

  - A flaw memory leak in the Linux kernel performance monitoring subsystem was found in the way if using
    PERF_EVENT_IOC_SET_FILTER. A local user could use this flaw to starve the resources causing denial of
    service. (CVE-2020-25704)

  - An issue was discovered in the Linux kernel through 5.9.1, as used with Xen through 4.14.x. Guest OS users
    can cause a denial of service (host OS hang) via a high rate of events to dom0, aka CID-e99502f76271.
    (CVE-2020-27673)

  - An issue was discovered in the Linux kernel through 5.9.1, as used with Xen through 4.14.x.
    drivers/xen/events/events_base.c allows event-channel removal during the event-handling loop (a race
    condition). This can cause a use-after-free or NULL pointer dereference, as demonstrated by a dom0 crash
    via events for an in-reconfiguration paravirtualized device, aka CID-073d0552ead5. (CVE-2020-27675)

  - A flaw was found in the way RTAS handled memory accesses in userspace to kernel communication. On a locked
    down (usually due to Secure Boot) guest system running on top of PowerVM or KVM hypervisors (pseries
    platform) a root like local user could use this flaw to further increase their privileges to that of a
    running kernel. (CVE-2020-27777)

  - A flaw was found in the JFS filesystem code in the Linux Kernel which allows a local attacker with the
    ability to set extended attributes to panic the system, causing memory corruption or escalating
    privileges. The highest threat from this vulnerability is to confidentiality, integrity, as well as system
    availability. (CVE-2020-27815)

  - A vulnerability was found in Linux Kernel where in the spk_ttyio_receive_buf2() function, it would
    dereference spk_ttyio_synth without checking whether it is NULL or not, and may lead to a NULL-ptr deref
    crash. (CVE-2020-27830)

  - A use after free in the Linux kernel infiniband hfi1 driver in versions prior to 5.10-rc6 was found in the
    way user calls Ioctl after open dev file and fork. A local user could use this flaw to crash the system.
    (CVE-2020-27835)

  - An information disclosure vulnerability exists in the /proc/pid/syscall functionality of Linux Kernel 5.1
    Stable and 5.4.66. More specifically, this issue has been introduced in v5.1-rc4 (commit
    631b7abacd02b88f4b0795c08b54ad4fc3e7c7c0) and is still present in v5.10-rc4, so it's likely that all
    versions in between are affected. An attacker can read /proc/pid/syscall to trigger this vulnerability,
    which leads to the kernel leaking memory contents. (CVE-2020-28588)

  - An issue was discovered in drivers/accessibility/speakup/spk_ttyio.c in the Linux kernel through 5.9.9.
    Local attackers on systems with the speakup driver could cause a local denial of service attack, aka
    CID-d41227544427. This occurs because of an invalid free when the line discipline is used more than once.
    (CVE-2020-28941)

  - A slab-out-of-bounds read in fbcon in the Linux kernel before 5.9.7 could be used by local attackers to
    read privileged information or potentially crash the kernel, aka CID-3c4e0dff2095. This occurs because
    KD_FONT_OP_COPY in drivers/tty/vt/vt.c can be used for manipulations such as font height. (CVE-2020-28974)

  - An issue was discovered in Xen through 4.14.x. Some OSes (such as Linux, FreeBSD, and NetBSD) are
    processing watch events using a single thread. If the events are received faster than the thread is able
    to handle, they will get queued. As the queue is unbounded, a guest may be able to trigger an OOM in the
    backend. All systems with a FreeBSD, Linux, or NetBSD (any version) dom0 are vulnerable. (CVE-2020-29568)

  - An issue was discovered in the Linux kernel through 5.10.1, as used with Xen through 4.14.x. The Linux
    kernel PV block backend expects the kernel thread handler to reset ring->xenblkd to NULL when stopped.
    However, the handler may not have time to run if the frontend quickly toggles between the states connect
    and disconnect. As a consequence, the block backend may re-use a pointer after it was freed. A misbehaving
    guest can trigger a dom0 crash by continuously connecting / disconnecting a block frontend. Privilege
    escalation and information leaks cannot be ruled out. This only affects systems with a Linux blkback.
    (CVE-2020-29569)

  - A locking inconsistency issue was discovered in the tty subsystem of the Linux kernel through 5.9.13.
    drivers/tty/tty_io.c and drivers/tty/tty_jobctrl.c may allow a read-after-free attack against TIOCGSID,
    aka CID-c8bcd9c5be24. (CVE-2020-29660)

  - A locking issue was discovered in the tty subsystem of the Linux kernel through 5.9.13.
    drivers/tty/tty_jobctrl.c allows a use-after-free attack against TIOCSPGRP, aka CID-54ffccbf053b.
    (CVE-2020-29661)

  - A flaw possibility of race condition and incorrect initialization of the process id was found in the Linux
    kernel child/parent process identification handling while filtering signal handlers. A local attacker is
    able to abuse this flaw to bypass checks to send any signal to a privileged process. (CVE-2020-35508)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version
number.");
  script_set_attribute(attribute:"see_also", value:"https://ubuntu.com/security/notices/USN-4751-1");
  script_set_attribute(attribute:"solution", value:
"Update the affected kernel package.");
  script_set_cvss_base_vector("CVSS2#AV:L/AC:L/Au:N/C:C/I:C/A:C");
  script_set_cvss_temporal_vector("CVSS2#E:POC/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:P/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2020-29661");
  script_set_attribute(attribute:"cvss3_score_source", value:"CVE-2020-29569");

  script_set_attribute(attribute:"exploitability_ease", value:"Exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"true");

  script_set_attribute(attribute:"vuln_publication_date", value:"2020/10/22");
  script_set_attribute(attribute:"patch_publication_date", value:"2021/02/25");
  script_set_attribute(attribute:"plugin_publication_date", value:"2021/03/23");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:canonical:ubuntu_linux:20.04:-:lts");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.8.0-44-generic");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.8.0-44-generic-lpae");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:canonical:ubuntu_linux:linux-image-5.8.0-44-lowlatency");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Ubuntu Local Security Checks");

  script_copyright(english:"Ubuntu Security Notice (C) 2021-2024 Canonical, Inc. / NASL script (C) 2021-2024 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info.nasl", "linux_alt_patch_detect.nasl");
  script_require_keys("Host/cpu", "Host/Ubuntu", "Host/Ubuntu/release", "Host/Debian/dpkg-l");

  exit(0);
}

include('debian_package.inc');
include('ksplice.inc');

if ( ! get_kb_item('Host/local_checks_enabled') ) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
var os_release = get_kb_item('Host/Ubuntu/release');
if ( isnull(os_release) ) audit(AUDIT_OS_NOT, 'Ubuntu');
os_release = chomp(os_release);
if (! ('20.04' >< os_release)) audit(AUDIT_OS_NOT, 'Ubuntu 20.04', 'Ubuntu ' + os_release);
if ( ! get_kb_item('Host/Debian/dpkg-l') ) audit(AUDIT_PACKAGE_LIST_MISSING);

var cpu = get_kb_item('Host/cpu');
if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
if ('x86_64' >!< cpu && cpu !~ "^i[3-6]86$" && 's390' >!< cpu && 'aarch64' >!< cpu) audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, 'Ubuntu', cpu);

var kernel_mappings = {
  '20.04': {
    '5.8.0': {
      'generic': '5.8.0-44',
      'generic-lpae': '5.8.0-44',
      'lowlatency': '5.8.0-44'
    }
  }
};

var host_kernel_release = get_kb_item('Host/uptrack-uname-r');
if (empty_or_null(host_kernel_release)) host_kernel_release = get_kb_item_or_exit('Host/uname-r');
var host_kernel_base_version = get_kb_item_or_exit('Host/Debian/kernel-base-version');
var host_kernel_type = get_kb_item_or_exit('Host/Debian/kernel-type');
if(empty_or_null(kernel_mappings[os_release][host_kernel_base_version][host_kernel_type])) audit(AUDIT_INST_VER_NOT_VULN, 'kernel ' + host_kernel_release);

var extra = '';
var kernel_fixed_version = kernel_mappings[os_release][host_kernel_base_version][host_kernel_type] + "-" + host_kernel_type;
if (deb_ver_cmp(ver1:host_kernel_release, ver2:kernel_fixed_version) < 0)
{
  extra = extra + 'Running Kernel level of ' + host_kernel_release + ' does not meet the minimum fixed level of ' + kernel_fixed_version + ' for this advisory.\n\n';
}
  else
{
  audit(AUDIT_PATCH_INSTALLED, 'Kernel package for USN-4751-1');
}

if (get_one_kb_item('Host/ksplice/kernel-cves'))
{
  var cve_list = make_list('CVE-2020-25656', 'CVE-2020-25668', 'CVE-2020-25669', 'CVE-2020-25704', 'CVE-2020-27673', 'CVE-2020-27675', 'CVE-2020-27777', 'CVE-2020-27815', 'CVE-2020-27830', 'CVE-2020-27835', 'CVE-2020-28588', 'CVE-2020-28941', 'CVE-2020-28974', 'CVE-2020-29568', 'CVE-2020-29569', 'CVE-2020-29660', 'CVE-2020-29661', 'CVE-2020-35508');
  if (ksplice_cves_check(cve_list))
  {
    audit(AUDIT_PATCH_INSTALLED, 'KSplice hotfix for USN-4751-1');
  }
  else
  {
    extra = extra + ksplice_reporting_text();
  }
}
if (extra) {
  security_report_v4(
    port       : 0,
    severity   : SECURITY_HOLE,
    extra      : extra
  );
  exit(0);
}