Unity Linux 20.1050a Security Update: kernel (UTSA-2026-100735)

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

include('compat.inc');

if (description)
{
  script_id(337033);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/08/17");

  script_cve_id("CVE-2026-45866");

  script_name(english:"Unity Linux 20.1050a Security Update: kernel (UTSA-2026-100735)");

  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-2026-100735 advisory.

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

    serial: caif: fix use-after-free in caif_serial ldisc_close()

    There is a use-after-free bug in caif_serial where handle_tx() may
    access ser->tty after the tty has been freed.

    The race condition occurs between ldisc_close() and packet transmission:

        CPU 0 (close)                     CPU 1 (xmit)
        -------------                     ------------
        ldisc_close()
          tty_kref_put(ser->tty)
          [tty may be freed here]
                         <-- race window -->
                                          caif_xmit()
                                            handle_tx()
                                              tty = ser->tty  // dangling ptr
                                              tty->ops->write() // UAF!
          schedule_work()
            ser_release()
              unregister_netdevice()

    The root cause is that tty_kref_put() is called in ldisc_close() while
    the network device is still active and can receive packets.

    Since ser and tty have a 1:1 binding relationship with consistent
    lifecycles (ser is allocated in ldisc_open and freed in ser_release
    via unregister_netdevice, and each ser binds exactly one tty), we can
    safely defer the tty reference release to ser_release() where the
    network device is unregistered.

    Fix this by moving tty_kref_put() from ldisc_close() to ser_release(),
    after unregister_netdevice(). This ensures the tty reference is held
    as long as the network device exists, preventing the UAF.

    Note: We save ser->tty before unregister_netdevice() because ser is
    embedded in netdev's private data and will be freed along with netdev
    (needs_free_netdev = true).

    How to reproduce: Add mdelay(500) at the beginning of ldisc_close()
    to widen the race window, then run the reproducer program [1].

    Note: There is a separate deadloop issue in handle_tx() when using
    PORT_UNKNOWN serial ports (e.g., /dev/ttyS3 in QEMU without proper
    serial backend). This deadloop exists even without this patch,
    and is likely caused by inconsistency between uart_write_room() and
    uart_write() in serial core. It has been addressed in a separate
    patch [2].

    KASAN report:

    ==================================================================
    BUG: KASAN: slab-use-after-free in handle_tx+0x5d1/0x620
    Read of size 1 at addr ffff8881131e1490 by task caif_uaf_trigge/9929

    Call Trace:
     <TASK>
     dump_stack_lvl+0x10e/0x1f0
     print_report+0xd0/0x630
     kasan_report+0xe4/0x120
     handle_tx+0x5d1/0x620
     dev_hard_start_xmit+0x9d/0x6c0
     __dev_queue_xmit+0x6e2/0x4410
     packet_xmit+0x243/0x360
     packet_sendmsg+0x26cf/0x5500
     __sys_sendto+0x4a3/0x520
     __x64_sys_sendto+0xe0/0x1c0
     do_syscall_64+0xc9/0xf80
     entry_SYSCALL_64_after_hwframe+0x77/0x7f
    RIP: 0033:0x7f615df2c0d7

    Allocated by task 9930:

    Freed by task 64:

    Last potentially related work creation:

    The buggy address belongs to the object at ffff8881131e1000
     which belongs to the cache kmalloc-cg-2k of size 2048
    The buggy address is located 1168 bytes inside of
     freed 2048-byte region [ffff8881131e1000, ffff8881131e1800)

    The buggy address belongs to the physical page:
    page_owner tracks the page as allocated
    page last free pid 9778 tgid 9778 stack trace:

    Memory state around the buggy address:
     ffff8881131e1380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
     ffff8881131e1400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
    >ffff8881131e1480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                             ^
     ffff8881131e1500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
     ffff8881131e1580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
    ==================================================================
    [1]: https://gist.github.com/mrpre/f683f244544f7b11e7fa87df9e6c2eeb
    [2]: https://lore.kernel.org/linux-serial/[email protected]/T/#u

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-2026-100735
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?6266790d");
  # https://lore.kernel.org/linux-cve-announce/2026052712-CVE-2026-45866-268a@gregkh
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?abbee99a");
  script_set_attribute(attribute:"see_also", value:"https://nvd.nist.gov/vuln/detail/CVE-2026-45866");
  script_set_attribute(attribute:"solution", value:
"Update the affected kernel package.");
  script_set_cvss_base_vector("CVSS2#AV:L/AC:L/Au:S/C:C/I:C/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:H/I:H/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-2026-45866");

  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:"2026/03/12");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/08/13");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/08/17");

  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 && 'x86_64' >!< cpu) audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, 'UOS Server', cpu);


var constraints = [
  {
    'release': '20',
    'sp': '1050a',
    'pkgs': [
      {'reference':'kernel-5.10.0-27.18.uelc20', 'sp':'1050a', 'cpu':'aarch64', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'kernel-5.10.0-27.18.uelc20', 'sp':'1050a', 'cpu':'amd64', 'rpm_spec_vers_cmp':TRUE},
      {'reference':'kernel-5.10.0-27.18.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');
}