Linux Distros Unpatched Vulnerability : CVE-2021-47371

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

include('compat.inc');

if (description)
{
  script_id(246500);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2025/08/09");

  script_cve_id("CVE-2021-47371");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2021-47371");

  script_set_attribute(attribute:"synopsis", value:
"The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be
patched.");
  script_set_attribute(attribute:"description", value:
"The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied
patch available.

  - In the Linux kernel, the following vulnerability has been resolved: nexthop: Fix memory leaks in nexthop
    notification chain listeners syzkaller discovered memory leaks [1] that can be reduced to the following
    commands: # ip nexthop add id 1 blackhole # devlink dev reload pci/0000:06:00.0 As part of the reload
    flow, mlxsw will unregister its netdevs and then unregister from the nexthop notification chain. Before
    unregistering from the notification chain, mlxsw will receive delete notifications for nexthop objects
    using netdevs registered by mlxsw or their uppers. mlxsw will not receive notifications for nexthops using
    netdevs that are not dismantled as part of the reload flow. For example, the blackhole nexthop above that
    internally uses the loopback netdev as its nexthop device. One way to fix this problem is to have
    listeners flush their nexthop tables after unregistering from the notification chain. This is error-prone
    as evident by this patch and also not symmetric with the registration path where a listener receives a
    dump of all the existing nexthops. Therefore, fix this problem by replaying delete notifications for the
    listener being unregistered. This is symmetric to the registration path and also consistent with the
    netdev notification chain. The above means that unregister_nexthop_notifier(), like
    register_nexthop_notifier(), will have to take RTNL in order to iterate over the existing nexthops and
    that any callers of the function cannot hold RTNL. This is true for mlxsw and netdevsim, but not for the
    VXLAN driver. To avoid a deadlock, change the latter to unregister its nexthop listener without holding
    RTNL, making it symmetric to the registration path. [1] unreferenced object 0xffff88806173d600 (size 512):
    comm syz-executor.0, pid 1290, jiffies 4295583142 (age 143.507s) hex dump (first 32 bytes): 41 9d 1e 60
    80 88 ff ff 08 d6 73 61 80 88 ff ff A..`......sa.... 08 d6 73 61 80 88 ff ff 01 00 00 00 00 00 00 00
    ..sa............ backtrace: [<ffffffff81a6b576>] kmemleak_alloc_recursive include/linux/kmemleak.h:43
    [inline] [<ffffffff81a6b576>] slab_post_alloc_hook+0x96/0x490 mm/slab.h:522 [<ffffffff81a716d3>]
    slab_alloc_node mm/slub.c:3206 [inline] [<ffffffff81a716d3>] slab_alloc mm/slub.c:3214 [inline]
    [<ffffffff81a716d3>] kmem_cache_alloc_trace+0x163/0x370 mm/slub.c:3231 [<ffffffff82e8681a>] kmalloc
    include/linux/slab.h:591 [inline] [<ffffffff82e8681a>] kzalloc include/linux/slab.h:721 [inline]
    [<ffffffff82e8681a>] mlxsw_sp_nexthop_obj_group_create
    drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:4918 [inline] [<ffffffff82e8681a>]
    mlxsw_sp_nexthop_obj_new drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:5054 [inline]
    [<ffffffff82e8681a>] mlxsw_sp_nexthop_obj_event+0x59a/0x2910
    drivers/net/ethernet/mellanox/mlxsw/spectrum_router.c:5239 [<ffffffff813ef67d>]
    notifier_call_chain+0xbd/0x210 kernel/notifier.c:83 [<ffffffff813f0662>] blocking_notifier_call_chain
    kernel/notifier.c:318 [inline] [<ffffffff813f0662>] blocking_notifier_call_chain+0x72/0xa0
    kernel/notifier.c:306 [<ffffffff8384b9c6>] call_nexthop_notifiers+0x156/0x310 net/ipv4/nexthop.c:244
    [<ffffffff83852bd8>] insert_nexthop net/ipv4/nexthop.c:2336 [inline] [<ffffffff83852bd8>] nexthop_add
    net/ipv4/nexthop.c:2644 [inline] [<ffffffff83852bd8>] rtm_new_nexthop+0x14e8/0x4d10
    net/ipv4/nexthop.c:2913 [<ffffffff833e9a78>] rtnetlink_rcv_msg+0x448/0xbf0 net/core/rtnetlink.c:5572
    [<ffffffff83608703>] netlink_rcv_skb+0x173/0x480 net/netlink/af_netlink.c:2504 [<ffffffff833de032>]
    rtnetlink_rcv+0x22/0x30 net/core/rtnetlink.c:5590 [<ffffffff836069de>] netlink_unicast_kernel
    net/netlink/af_netlink.c:1314 [inline] [<ffffffff836069de>] netlink_unicast+0x5ae/0x7f0
    net/netlink/af_netlink.c:1340 [<ffffffff83607501>] netlink_sendmsg+0x8e1/0xe30
    net/netlink/af_netlink.c:1929 [<ffffffff832fde84>] sock_sendmsg_nosec net/socket.c:704 [inline
    ---truncated--- (CVE-2021-47371)

Note that Nessus relies on the presence of the package as reported by the vendor.");
  script_set_attribute(attribute:"see_also", value:"https://ubuntu.com/security/CVE-2021-47371");
  script_set_attribute(attribute:"solution", value:
"There is no known solution at this time.");
  script_set_attribute(attribute:"agent", value:"unix");
  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:L/UI:N/S:U/C:N/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-2021-47371");

  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"false");
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  script_set_attribute(attribute:"vuln_publication_date", value:"2024/05/21");
  script_set_attribute(attribute:"plugin_publication_date", value:"2025/08/09");

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  script_category(ACT_GATHER_INFO);
  script_family(english:"Misc.");

  script_copyright(english:"This script is Copyright (C) 2025 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info2.nasl", "set_linux_os_id.nasl");
  script_require_keys("Host/cpu", "Host/local_checks_enabled", "global_settings/vendor_unpatched", "Host/OS/identifier");
  script_require_ports("Host/OS/Ubuntu Linux-16.04", "Host/OS/Ubuntu Linux-18.04", "Host/OS/Ubuntu Linux-20.04", "Host/OS/Ubuntu Linux-22.04");

  exit(0);
}

if (!get_kb_item("global_settings/vendor_unpatched")) exit(0, "Unpatched Vulnerabilities Detection not active.");
if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
if (empty_or_null(get_one_kb_item("Host/Debian/dpkg-l"))) audit(AUDIT_PACKAGE_LIST_MISSING);

include('linux_unpatched.inc');

var distro_constraints_array = {
  "Ubuntu Linux-16.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "16.04",
        "pkgs": [
          {"reference": "linux-hwe-edge"}
        ]
      }
    ]
  },
  "Ubuntu Linux-18.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "18.04",
        "pkgs": [
          {"reference": "linux-aws-5.0"},
          {"reference": "linux-aws-5.3"},
          {"reference": "linux-azure-5.3"},
          {"reference": "linux-azure-cloud-tools-4.15.0"},
          {"reference": "linux-azure-edge"},
          {"reference": "linux-azure-headers-4.15.0"},
          {"reference": "linux-azure-tools-4.15.0"},
          {"reference": "linux-cloud-tools-4.15.0"},
          {"reference": "linux-gcp-5.3"},
          {"reference": "linux-gcp-headers-4.15.0"},
          {"reference": "linux-gcp-tools-4.15.0"},
          {"reference": "linux-gke-4.15"},
          {"reference": "linux-gke-5.4"},
          {"reference": "linux-gkeop-5.4"},
          {"reference": "linux-headers-4.15.0"},
          {"reference": "linux-hwe"},
          {"reference": "linux-hwe-edge"},
          {"reference": "linux-image-4.15.0"},
          {"reference": "linux-image-unsigned-4.15.0"},
          {"reference": "linux-modules-4.15.0"},
          {"reference": "linux-modules-extra-4.15.0"},
          {"reference": "linux-oem-headers-4.15.0"},
          {"reference": "linux-oem-tools-4.15.0"},
          {"reference": "linux-oracle-5.0"},
          {"reference": "linux-oracle-5.3"},
          {"reference": "linux-tools-4.15.0"},
          {"reference": "linux-udebs-azure"},
          {"reference": "linux-udebs-oem"}
        ]
      }
    ]
  },
  "Ubuntu Linux-20.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "20.04",
        "pkgs": [
          {"reference": "linux-aws-5.11"},
          {"reference": "linux-aws-5.13"},
          {"reference": "linux-aws-5.8"},
          {"reference": "linux-azure-5.11"},
          {"reference": "linux-azure-5.13"},
          {"reference": "linux-azure-5.8"},
          {"reference": "linux-azure-fde"},
          {"reference": "linux-buildinfo-5.4.0"},
          {"reference": "linux-buildinfo-5.6.0"},
          {"reference": "linux-cloud-tools-5.4.0"},
          {"reference": "linux-cloud-tools-5.6.0"},
          {"reference": "linux-gcp-5.11"},
          {"reference": "linux-gcp-5.13"},
          {"reference": "linux-gcp-5.8"},
          {"reference": "linux-gke"},
          {"reference": "linux-gke-5.15"},
          {"reference": "linux-headers-5.4.0"},
          {"reference": "linux-headers-5.6.0"},
          {"reference": "linux-hwe-5.11"},
          {"reference": "linux-hwe-5.13"},
          {"reference": "linux-hwe-5.8"},
          {"reference": "linux-image-5.4.0"},
          {"reference": "linux-image-unsigned-5.6.0"},
          {"reference": "linux-intel-5.13"},
          {"reference": "linux-libc-dev"},
          {"reference": "linux-modules-5.4.0"},
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          {"reference": "linux-modules-extra-5.6.0"},
          {"reference": "linux-oem-5.10"},
          {"reference": "linux-oem-5.13"},
          {"reference": "linux-oem-5.14"},
          {"reference": "linux-oem-5.6-headers-5.6.0"},
          {"reference": "linux-oem-5.6-tools-5.6.0"},
          {"reference": "linux-oem-5.6-tools-common"},
          {"reference": "linux-oem-5.6-tools-host"},
          {"reference": "linux-oracle-5.11"},
          {"reference": "linux-oracle-5.13"},
          {"reference": "linux-oracle-5.8"},
          {"reference": "linux-raspi2"},
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          {"reference": "linux-riscv-tools-5.4.0"},
          {"reference": "linux-tools-5.4.0"},
          {"reference": "linux-tools-5.6.0"},
          {"reference": "linux-udebs-generic"},
          {"reference": "linux-udebs-oem"}
        ]
      }
    ]
  },
  "Ubuntu Linux-22.04": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "22.04",
        "pkgs": [
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          {"reference": "linux-aws-5.19"},
          {"reference": "linux-aws-6.2"},
          {"reference": "linux-azure-5.19"},
          {"reference": "linux-azure-6.2"},
          {"reference": "linux-azure-fde-5.19"},
          {"reference": "linux-azure-fde-6.2"},
          {"reference": "linux-buildinfo-5.15.0"},
          {"reference": "linux-buildinfo-5.17.0"},
          {"reference": "linux-cloud-tools-5.15.0"},
          {"reference": "linux-cloud-tools-5.17.0"},
          {"reference": "linux-gcp-5.19"},
          {"reference": "linux-gcp-6.2"},
          {"reference": "linux-headers-5.15.0"},
          {"reference": "linux-headers-5.17.0"},
          {"reference": "linux-hwe-5.19"},
          {"reference": "linux-hwe-6.2"},
          {"reference": "linux-image-5.15.0"},
          {"reference": "linux-image-unsigned-5.17.0"},
          {"reference": "linux-lowlatency-hwe-5.19"},
          {"reference": "linux-lowlatency-hwe-6.2"},
          {"reference": "linux-modules-5.15.0"},
          {"reference": "linux-modules-5.17.0"},
          {"reference": "linux-modules-extra-5.15.0"},
          {"reference": "linux-modules-extra-5.17.0"},
          {"reference": "linux-nvidia-6.2"},
          {"reference": "linux-oem-5.17-headers-5.17.0"},
          {"reference": "linux-oem-5.17-tools-5.17.0"},
          {"reference": "linux-oem-5.17-tools-host"},
          {"reference": "linux-oem-6.0"},
          {"reference": "linux-oem-6.1"},
          {"reference": "linux-riscv-5.19"},
          {"reference": "linux-riscv-headers-5.15.0"},
          {"reference": "linux-riscv-tools-5.15.0"},
          {"reference": "linux-starfive-5.19"},
          {"reference": "linux-starfive-6.2"},
          {"reference": "linux-tools-5.15.0"},
          {"reference": "linux-tools-5.17.0"}
        ]
      }
    ]
  }
};

var distro_constraints_values = linux_unpatched::get_distro_constraints(distro_constraints_arr:distro_constraints_array);
if (empty_or_null(distro_constraints_values)) audit(AUDIT_HOST_NOT, 'affected');
var report = linux_unpatched::check_unpatched_constraints(distro_constraints_values:distro_constraints_values);

if (!empty_or_null(report))
{
  security_report_v4(
      port       : 0,
      severity   : SECURITY_WARNING,
      extra      : report
  );
  exit(0);
}
else
{
  audit(AUDIT_HOST_NOT, 'affected');
}