Linux Distros Unpatched Vulnerability : CVE-2026-74656

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

include('compat.inc');

if (description)
{
  script_id(338963);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/08/22");

  script_cve_id("CVE-2026-74656");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2026-74656");

  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.

  - ipv4: fix use-after-free in fib_nhc_update_mtu() fib_nhc_update_mtu() walks the nexthop exception table
    under RTNL, but RTNL does not serialize this walk with PMTU exception updates. The walk uses
    rcu_dereference_protected() with a constant true condition without holding fnhe_lock. The following
    interleaving can therefore occur: CPU 0 CPU 1 fib_nhc_update_mtu() update_or_create_fnhe() load fnhe
    spin_lock_bh(&fnhe_lock) fnhe_remove_oldest() unlink fnhe kfree_rcu(fnhe, rcu) <quiescent state> access
    fnhe after grace period KASAN reported: BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410
    Read of size 8 at addr ffff888107d49000 by task poc/90 Call Trace: fib_nhc_update_mtu+0x3df/0x410
    fib_sync_mtu+0x7a/0xd0 fib_netdev_event+0x229/0x3f0 netif_set_mtu_ext+0x33a/0x570 dev_set_mtu+0x88/0x120
    The same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a pair and other writers serialize
    them with fnhe_lock. RCU alone prevents reclamation, but would still allow concurrent writers to leave a
    mixed pair. Walk the table under RCU and acquire fnhe_lock only while updating each exception. RCU keeps
    the current entry alive while the short critical section serializes its paired PMTU fields. This avoids
    holding the global lock while scanning all 2048 buckets for every nexthop. (CVE-2026-74656)

Note that Nessus relies on the presence of the package as reported by the vendor.");
  script_set_attribute(attribute:"see_also", value:"https://security-tracker.debian.org/tracker/CVE-2026-74656");
  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:N/AC:L/Au:N/C:P/I:P/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:U/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:U/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-74656");

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

  script_set_attribute(attribute:"vuln_publication_date", value:"2026/08/22");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/08/22");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:11.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:12.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:13.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:14.0");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:linux");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

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

  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", "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/Debian Linux-11", "Host/OS/Debian Linux-12", "Host/OS/Debian Linux-13", "Host/OS/Debian Linux-14");

  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 = {
  "Debian Linux-12": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "12",
        "pkgs": [
          {"reference": "btrfs-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "cdrom-core-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "ext4-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "fat-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "isofs-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "jfs-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "kernel-image-6.1.0-50-alpha-generic-di"},
          {"reference": "linux-doc"},
          {"reference": "linux-doc-6.1"},
          {"reference": "linux-headers-6.1.0"},
          {"reference": "linux-source"},
          {"reference": "linux-source-6.1"},
          {"reference": "linux-support-6.1.0"},
          {"reference": "loop-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "nic-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "nic-shared-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "nic-wireless-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "pata-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "ppp-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "scsi-core-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "scsi-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "scsi-nic-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "serial-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "usb-serial-modules-6.1.0-50-alpha-generic-di"},
          {"reference": "xfs-modules-6.1.0-50-alpha-generic-di"}
        ]
      }
    ]
  },
  "Debian Linux-11": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "11",
        "pkgs": [
          {"reference": "bpftool"},
          {"reference": "btrfs-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "cdrom-core-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "hyperv-daemons"},
          {"reference": "kernel-image-5.10.0-32-alpha-generic-di"},
          {"reference": "libcpupower-dev"},
          {"reference": "libcpupower1"},
          {"reference": "linux-bootwrapper-5.10.0"},
          {"reference": "linux-config-5.10"},
          {"reference": "linux-cpupower"},
          {"reference": "linux-doc"},
          {"reference": "linux-doc-5.10"},
          {"reference": "linux-headers-5.10.0"},
          {"reference": "linux-kbuild-5.10"},
          {"reference": "linux-libc-dev"},
          {"reference": "linux-perf"},
          {"reference": "linux-perf-5.10"},
          {"reference": "linux-source"},
          {"reference": "linux-source-5.10"},
          {"reference": "linux-support-5.10.0"},
          {"reference": "loop-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "nic-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "nic-shared-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "nic-wireless-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "pata-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "ppp-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "scsi-core-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "scsi-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "scsi-nic-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "serial-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "usb-serial-modules-5.10.0-32-alpha-generic-di"},
          {"reference": "usbip"}
        ]
      }
    ]
  },
  "Debian Linux-14": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "14",
        "pkgs": [
          {"reference": "bpftool"},
          {"reference": "hyperv-daemons"},
          {"reference": "intel-sdsi"},
          {"reference": "libcpupower-dev"},
          {"reference": "libcpupower1"},
          {"reference": "linux-base-7.1.8+deb14.1-alpha-generic"},
          {"reference": "linux-base-7.1.8+deb14.1-alpha-smp"},
          {"reference": "linux-base-7.1.8+deb14.1-amd64"},
          {"reference": "linux-base-7.1.8+deb14.1-arm64"},
          {"reference": "linux-base-7.1.8+deb14.1-arm64-16k"},
          {"reference": "linux-base-7.1.8+deb14.1-armmp"},
          {"reference": "linux-base-7.1.8+deb14.1-armmp-lpae"},
          {"reference": "linux-base-7.1.8+deb14.1-cloud-amd64"},
          {"reference": "linux-base-7.1.8+deb14.1-cloud-arm64"},
          {"reference": "linux-base-7.1.8+deb14.1-loong64"},
          {"reference": "linux-base-7.1.8+deb14.1-m68k"},
          {"reference": "linux-base-7.1.8+deb14.1-parisc"},
          {"reference": "linux-base-7.1.8+deb14.1-parisc64"},
          {"reference": "linux-base-7.1.8+deb14.1-powerpc"},
          {"reference": "linux-base-7.1.8+deb14.1-powerpc-smp"},
          {"reference": "linux-base-7.1.8+deb14.1-powerpc64"},
          {"reference": "linux-base-7.1.8+deb14.1-powerpc64-64k"},
          {"reference": "linux-base-7.1.8+deb14.1-powerpc64le"},
          {"reference": "linux-base-7.1.8+deb14.1-powerpc64le-64k"},
          {"reference": "linux-base-7.1.8+deb14.1-riscv64"},
          {"reference": "linux-base-7.1.8+deb14.1-rt-amd64"},
          {"reference": "linux-base-7.1.8+deb14.1-rt-arm64"},
          {"reference": "linux-base-7.1.8+deb14.1-s390x"},
          {"reference": "linux-base-7.1.8+deb14.1-sh7751r"},
          {"reference": "linux-base-7.1.8+deb14.1-sparc64"}
        ]
      }
    ]
  },
  "Debian Linux-13": {
    "package_manager": "dpkg-l",
    "constraints": [
      {
        "release": "13",
        "pkgs": [
          {"reference": "bpftool"},
          {"reference": "hyperv-daemons"},
          {"reference": "intel-sdsi"},
          {"reference": "libcpupower-dev"},
          {"reference": "libcpupower1"},
          {"reference": "linux-bpf-dev"},
          {"reference": "linux-config-6.12"},
          {"reference": "linux-cpupower"},
          {"reference": "linux-doc"},
          {"reference": "linux-doc-6.12"},
          {"reference": "linux-headers-4kc-malta"},
          {"reference": "linux-headers-5kc-malta"},
          {"reference": "linux-headers-6.12.94+deb13-4kc-malta"},
          {"reference": "linux-headers-6.12.94+deb13-5kc-malta"},
          {"reference": "linux-headers-6.12.94+deb13-alpha-generic"},
          {"reference": "linux-headers-6.12.94+deb13-alpha-smp"},
          {"reference": "linux-headers-6.12.94+deb13-amd64"},
          {"reference": "linux-headers-6.12.94+deb13-arm64"},
          {"reference": "linux-headers-6.12.94+deb13-arm64-16k"},
          {"reference": "linux-headers-6.12.94+deb13-armmp"},
          {"reference": "linux-headers-6.12.94+deb13-armmp-lpae"},
          {"reference": "linux-headers-6.12.94+deb13-cloud-amd64"},
          {"reference": "linux-headers-6.12.94+deb13-cloud-arm64"},
          {"reference": "linux-headers-6.12.94+deb13-common"},
          {"reference": "linux-headers-6.12.94+deb13-common-rt"},
          {"reference": "linux-headers-6.12.94+deb13-loong64"},
          {"reference": "linux-headers-6.12.94+deb13-loongson-3"},
          {"reference": "linux-headers-6.12.94+deb13-m68k"},
          {"reference": "linux-headers-6.12.94+deb13-mips32r2eb"},
          {"reference": "linux-headers-6.12.94+deb13-mips32r2el"},
          {"reference": "linux-headers-6.12.94+deb13-mips64r2eb"},
          {"reference": "linux-headers-6.12.94+deb13-mips64r2el"}
        ]
      }
    ]
  }
};

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 third_party_support = get_kb_item('Host/OS/extended-third-party');
if (!empty_or_null(third_party_support)) {
    var third_party_vendors = distro_constraints_values['third_party'];
    if (!empty_or_null(third_party_vendors)) {
        var vendor;
        foreach vendor (third_party_vendors) {
            if (vendor == third_party_support) exit(0, 'A third party management patch is available for this vulnerability from ' + vendor + '.\n');
        }
    }
}

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');
}