Unity Linux 20.1050a Security Update: kernel (UTSA-2026-098841)

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

include('compat.inc');

if (description)
{
  script_id(340344);
  script_version("1.2");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/08/28");

  script_cve_id("CVE-2026-23086");

  script_name(english:"Unity Linux 20.1050a Security Update: kernel (UTSA-2026-098841)");

  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-2026-098841 advisory.

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

    vsock/virtio: cap TX credit to local buffer size

    The virtio transports derives its TX credit directly from peer_buf_alloc,
    which is set from the remote endpoint's SO_VM_SOCKETS_BUFFER_SIZE value.

    On the host side this means that the amount of data we are willing to
    queue for a connection is scaled by a guest-chosen buffer size, rather
    than the host's own vsock configuration. A malicious guest can advertise
    a large buffer and read slowly, causing the host to allocate a
    correspondingly large amount of sk_buff memory.
    The same thing would happen in the guest with a malicious host, since
    virtio transports share the same code base.

    Introduce a small helper, virtio_transport_tx_buf_size(), that
    returns min(peer_buf_alloc, buf_alloc), and use it wherever we consume
    peer_buf_alloc.

    This ensures the effective TX window is bounded by both the peer's
    advertised buffer and our own buf_alloc (already clamped to
    buffer_max_size via SO_VM_SOCKETS_BUFFER_MAX_SIZE), so a remote peer
    cannot force the other to queue more data than allowed by its own
    vsock settings.

    On an unpatched Ubuntu 22.04 host (~64 GiB RAM), running a PoC with
    32 guest vsock connections advertising 2 GiB each and reading slowly
    drove Slab/SUnreclaim from ~0.5 GiB to ~57 GiB; the system only
    recovered after killing the QEMU process. That said, if QEMU memory is
    limited with cgroups, the maximum memory used will be limited.

    With this patch applied:

      Before:
        MemFree:        ~61.6 GiB
        Slab:           ~142 MiB
        SUnreclaim:     ~117 MiB

      After 32 high-credit connections:
        MemFree:        ~61.5 GiB
        Slab:           ~178 MiB
        SUnreclaim:     ~152 MiB

    Only ~35 MiB increase in Slab/SUnreclaim, no host OOM, and the guest
    remains responsive.

    Compatibility with non-virtio transports:

      - VMCI uses the AF_VSOCK buffer knobs to size its queue pairs per
        socket based on the local vsk->buffer_* values; the remote side
        cannot enlarge those queues beyond what the local endpoint
        configured.

      - Hyper-V's vsock transport uses fixed-size VMBus ring buffers and
        an MTU bound; there is no peer-controlled credit field comparable
        to peer_buf_alloc, and the remote endpoint cannot drive in-flight
        kernel memory above those ring sizes.

      - The loopback path reuses virtio_transport_common.c, so it
        naturally follows the same semantics as the virtio transport.

    This change is limited to virtio_transport_common.c and thus affects
    virtio-vsock, vhost-vsock, and loopback, bringing them in line with the
    remote window intersected with local policy behaviour that VMCI and
    Hyper-V already effectively have.

    [Stefano: small adjustments after changing the previous patch]
    [Stefano: tweak the commit message]

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-2026-098841
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?46937f4f");
  # https://lore.kernel.org/linux-cve-announce/2026020423-CVE-2026-23086-9ad9@gregkh
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?ef8296ad");
  script_set_attribute(attribute:"see_also", value:"https://nvd.nist.gov/vuln/detail/CVE-2026-23086");
  script_set_attribute(attribute:"solution", value:
"Update the affected kernel package.");
  script_set_cvss_base_vector("CVSS2#AV:L/AC:L/Au:S/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:L/UI:N/S:U/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-2026-23086");

  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:"2026/02/04");
  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');
}