Linux Distros Unpatched Vulnerability : CVE-2026-98797

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

include('compat.inc');

if (description)
{
  script_id(367066);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/10/18");

  script_cve_id("CVE-2026-98797");

  script_name(english:"Linux Distros Unpatched Vulnerability : CVE-2026-98797");

  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.

  - net: cap skb->queue_mapping when the tx queue is picked skbedit can set skb->queue_mapping and raise the
    per-CPU skip_txqueue flag so __dev_queue_xmit() honours the mapping. __dev_queue_xmit() cleared the flag
    before sch_handle_egress() and only read it afterwards, so the flag was not confined to the xmit that set
    it: a nested xmit (mirred redirect or mirror, or a drop after skbedit) could set the flag and the outer
    xmit would consume it for an skb that never went through skbedit. A forwarded packet still carries the
    ingress NIC's rx_queue + 1 in skb->queue_mapping, so the outer device then indexes its tx queue state with
    that stale value. Taprio's child array q->qdiscs[] is sized to the device's queue count, so
    taprio_enqueue() indexes past its allocation and dereferences the result as a struct Qdisc *. We (ab)use
    the skb->nf_skip_egress which means skip netfilter egress for this packet to tag to am I in tc
    egress?. Despite the overload I dont see it as a conflict since the marker is set only around the single
    sch_handle_egress() call and ingress path is guarded by tc_at_ingress. I will send a followup(net-next)
    patch once this hits net-next to rename the skb->nf_skip_egress bit/flag to skb->skip_egress Arm the flag
    only from the egress classifier that can use it: raise skip_txqueue from tcf_skbedit_act() only when it
    runs inside sch_handle_egress(), thanks to skb->nf_skip_egress. An egress qdisc classifier runs in
    q->enqueue(), after the tx queue has been picked, so a mapping it sets cannot affect the current packet;
    arming the flag there only pollutes it for a later xmit. Then own the flag for the xmit frame the egress
    hook runs in: save the incoming value and clear it just before sch_handle_egress(), and restore it after
    the hook - on the consumed (drop) path, or, in the same call that reads it, on the surviving path. The
    save and the restores stay inside the egress_needed_key static branch, so a packet pays for them only when
    egress hooks are active (2f1e85b1aee4). Store the value netdev_cap_txqueue() selected back into
    skb->queue_mapping in netdev_tx_queue_mapping(), as netdev_core_pick_tx() already does, so the
    skip_txqueue path never hands a later reader on the xmit path a mapping the device cannot serve. A store
    made still later in the same frame, by a tc BPF program attached to a transmit qdisc, is outside this path
    and is not re-capped; a separate followup will resolve that path. netdev_xmit_skip_txqueue() returns the
    previous flag value so the save-and-clear is one call, and a no-op stub is provided when CONFIG_NET_EGRESS
    is disabled. skb->nf_skip_egress is compiled under CONFIG_NET_EGRESS rather than
    CONFIG_NETFILTER_SKIP_EGRESS, so skb_at_tc_egress() is valid whenever the egress path is built. A local
    user in a network namespace can redirect a packet from a device with more TX queues to one with fewer
    after setting a mapping valid only on the larger device. That reaches these reads and, under KASAN, faults
    with slab-out-of-bounds in taprio_enqueue. Conditions to recreate the bug: the report's own trigger is a
    local user with CAP_NET_ADMIN in a network namespace, so no eBPF program is needed. With
    CONFIG_NET_SCH_TAPRIO=y, CONFIG_NET_ACT_SKBEDIT=y, CONFIG_NET_ACT_MIRRED=y, CONFIG_NET_CLS_MATCHALL=y,
    CONFIG_NET_SCH_PRIO=y and KASAN enabled, create qa (3 queues), qb (2 queues) and qc (1 queue) as dummy
    devices; put a taprio root on qb (num_tc 1, queues 2@0) and clsact on all three; then add an egress
    matchall filter on every device. On qa: action skbedit queue_mapping 2 pipe action mirred egress redirect
    dev qb. On qb: action mirred egress mirror dev qc. On qc: action skbedit queue_mapping 0 pipe. Send
    one packet out qa. qc's skbedit sets the flag while qb's outer xmit is in flight; without the fix qb
    consumes it and reads its two-entry taprio child array with the forwarded packet's stale mapping. A qc
    whose skb ---truncated--- (CVE-2026-98797)

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-2026-98797");
  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-2026-98797");

  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:"2026/10/18");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/10/18");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:12.0");
  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-12");

  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"}
        ]
      }
    ]
  }
};

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');
}