Unity Linux 20.1050a Security Update: kernel (UTSA-2026-098883)

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
##

include('compat.inc');

if (description)
{
  script_id(340497);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/08/26");

  script_cve_id("CVE-2026-63806");

  script_name(english:"Unity Linux 20.1050a Security Update: kernel (UTSA-2026-098883)");

  script_set_attribute(attribute:"synopsis", value:
"The Unity Linux host is missing one or more security updates.");
  script_set_attribute(attribute:"description", value:
"The Unity Linux 20 host has a package installed that is affected by a vulnerability as referenced in the
UTSA-2026-098883 advisory.

    In the Linux kernel, the following vulnerability has been resolved:

    KVM: Replace guest-triggerable BUG_ON() in ioeventfd datamatch with get_unaligned()

    Drop a BUG_ON() that has been reachable since it was first added, way back
    in 2009, and instead use get_unaligned() to perform potentially-unaligned
    accesses.

    For a given store, KVM x86's emulator tracks the entire value in the
    destination operand, x86_emulate_ctxt.dst.  If the destination is memory,
    and the target splits multiple pages and/or is emulated MMIO, then KVM
    handles each fragment independently.  E.g. on a page split starting at page
    offset 0xffc, KVM writes 4 bytes to the first page, then the remaining
    bytes to the second page, using ctxt->dst as the source for both (with
    appropriate offsets).

    If the destination splits a page *and* hits emulated MMIO on the second
    page, then KVM will complete the write to the first page, then emulate the
    MMIO access to the second page.  If there is a datamatch-enabled ioeventfd
    at offset 0 of the second page, then KVM will process the remainder of the
    store as a potential ioeventfd signal.

    Putting it all together, if the guest emits a store that splits a page
    starting at page offset N, and the second page has a datamatch-enabled
    ioeventfd at offset 0, then KVM will check for datamatch using
    &dst.valptr[N] as the source.  Due to dst (and thus dst.valptr) being
    32-byte aligned, if N is not aligned to @len, the BUG_ON() fires.

    E.g. with a 16-byte store at page offset 0xffc, to an ioeventfd of len 8,
    all initial checks in ioeventfd_in_range() will succeed, and the BUG_ON()
    fires due to @val being 4-byte aligned, but not 8-byte aligned.

      ------------[ cut here ]------------
      kernel BUG at arch/x86/kvm/../../../virt/kvm/eventfd.c:783!
      Oops: invalid opcode: 0000 [#1] SMP
      CPU: 0 UID: 1000 PID: 615 Comm: repro Not tainted 7.1.0-rc2-ff238429d1ea #365 PREEMPT
      Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
      RIP: 0010:ioeventfd_write+0x6c/0x70 [kvm]
      Call Trace:
       <TASK>
       __kvm_io_bus_write+0x85/0xb0 [kvm]
       kvm_io_bus_write+0x53/0x80 [kvm]
       vcpu_mmio_write+0x66/0xf0 [kvm]
       emulator_read_write_onepage+0x12a/0x540 [kvm]
       emulator_read_write+0x109/0x2b0 [kvm]
       x86_emulate_insn+0x4f8/0xfb0 [kvm]
       x86_emulate_instruction+0x181/0x790 [kvm]
       kvm_mmu_page_fault+0x313/0x630 [kvm]
       vmx_handle_exit+0x18a/0x590 [kvm_intel]
       kvm_arch_vcpu_ioctl_run+0xc81/0x1c90 [kvm]
       kvm_vcpu_ioctl+0x2d5/0x970 [kvm]
       __x64_sys_ioctl+0x8a/0xd0
       do_syscall_64+0xb7/0x890
       entry_SYSCALL_64_after_hwframe+0x4b/0x53
      RIP: 0033:0x7f19c931a9bf
       </TASK>
      Modules linked in: kvm_intel kvm irqbypass
      ---[ end trace 0000000000000000 ]---

    In a perfect world, the fix would be to simply delete the BUG_ON(), as KVM
    x86 doesn't perform alignment checks on normal memory accesses at CPL0.
    Sadly, C99 ruins all the fun; while the x86 architecture plays nice,
    dereferencing an unaligned pointer directly is undefined behavior in C,
    e.g. triggers splats when running with CONFIG_UBSAN_ALIGNMENT=y.

Tenable has extracted the preceding description block directly from the Unity Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version
number.");
  # https://src.uniontech.com/#/security_advisory_detail?utsa_id=UTSA-2026-098883
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?7d703d8e");
  # https://lore.kernel.org/linux-cve-announce/2026071902-CVE-2026-63806-b5c7@gregkh
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?481bbcb2");
  script_set_attribute(attribute:"see_also", value:"https://nvd.nist.gov/vuln/detail/CVE-2026-63806");
  script_set_attribute(attribute:"solution", value:
"Update the affected kernel package.");
  script_set_cvss_base_vector("CVSS2#AV:L/AC:L/Au:N/C:N/I:N/A:C");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-63806");

  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"false");

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/07/08");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/08/10");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/08/26");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

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

  script_copyright(english:"This script is Copyright (C) 2026 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info2.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/UOS-Server/release", "Host/UOS-Server/rpm-list", "Host/cpu");

  exit(0);
}
include('rpm2.inc');

if (!get_kb_item('Host/local_checks_enabled')) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
var os_product = get_kb_item('installed_os/local/SSH/0/product');
if (isnull(os_product) || 'UOS Server' >!< os_product) audit(AUDIT_OS_NOT, 'UOS Server');
var os_version = get_kb_item('installed_os/local/SSH/0/version');
if (isnull(os_version)) audit(AUDIT_UNKNOWN_APP_VER, 'UOS Server');
if (! preg(pattern:"^20.1050a([^0-9]|$)", string:os_version)) audit(AUDIT_OS_NOT, 'UOS Server 20.1050a', 'UOS Server ' + os_version);

if (!get_kb_item('Host/UOS-Server/rpm-list')) audit(AUDIT_PACKAGE_LIST_MISSING);

var cpu = get_kb_item('Host/cpu');
if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
if ('aarch64' >!< cpu && 'amd64' >!< cpu && 'loongarch64' >!< cpu && 'x86_64' >!< cpu) audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, 'UOS Server', cpu);


var constraints = [
  {
    'release': '20',
    'sp': '1050a',
    'pkgs': [
      {'reference':'kernel-4.19.0-91.82.132.24.uelc20', 'sp':'1050a', 'cpu':'aarch64', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'kernel-4.19.0-91.82.132.24.uelc20', 'sp':'1050a', 'cpu':'amd64', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'kernel-4.19.0-91.82.132.24.uelc20', 'sp':'1050a', 'cpu':'loongarch64', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'kernel-4.19.0-91.82.132.24.uelc20', 'sp':'1050a', 'cpu':'x86_64', 'rpm_spec_vers_cmp':TRUE}
    ]
  }
];

var os_release = get_one_kb_item('installed_os/local/SSH/0/release');
var os_sp = get_one_kb_item('Host/*/minor_release');

var flag = 0;
var reference;
var sp;
var _cpu;
var el_string;
var rpm_spec_vers_cmp;
var epoch;
var allowmaj;
var exists_check;
var cves;
foreach var constraint ( constraints ) {
  # Check that the target release is equal to the affected release
  if (!empty_or_null(constraint['release'])){
    if (constraint['release'] != os_release) continue;
  }
  if (!empty_or_null(constraint['sp'])){
    if (constraint['sp'] != os_sp) continue;
  }
  foreach var pkg ( constraint['pkgs'] ) {
    reference = NULL;
    sp = NULL;
    _cpu = NULL;
    el_string = NULL;
    rpm_spec_vers_cmp = NULL;
    epoch = NULL;
    allowmaj = NULL;
    exists_check = NULL;
    cves = NULL;
    if (!empty_or_null(pkg['reference'])) reference = pkg['reference'];
    if (!empty_or_null(pkg['sp'])) sp = pkg['sp'];
    if (!empty_or_null(pkg['cpu'])) _cpu = pkg['cpu'];
    if (!empty_or_null(pkg['el_string'])) el_string = pkg['el_string'];
    if (!empty_or_null(pkg['rpm_spec_vers_cmp'])) rpm_spec_vers_cmp = pkg['rpm_spec_vers_cmp'];
    if (!empty_or_null(pkg['epoch'])) epoch = pkg['epoch'];
    if (!empty_or_null(pkg['allowmaj'])) allowmaj = pkg['allowmaj'];
    if (!empty_or_null(pkg['exists_check'])) exists_check = pkg['exists_check'];
    if (!empty_or_null(pkg['cves'])) cves = pkg['cves'];
    if (reference &&
        ## (no known rpm to check OR known rpm_exists)
        (!exists_check || rpm_exists(rpm:exists_check)) &&
        rpm_check(sp:sp, cpu:_cpu, reference:reference, epoch:epoch, el_string:el_string, rpm_spec_vers_cmp:rpm_spec_vers_cmp, allowmaj:allowmaj, cves:cves)) flag++;
  }
}


if (flag)
{
  security_report_v4(
      port       : 0,
      severity   : SECURITY_WARNING,
      extra      : rpm_report_get()
  );
  exit(0);
}
else
{
  var tested = pkg_tests_get();
  if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
  else audit(AUDIT_PACKAGE_NOT_INSTALLED, 'kernel');
}