{
  "cveId": "CVE-2026-98401",
  "url": "https://patchblox.com/security/cve/CVE-2026-98401",
  "summary": "CVE-2026-98401 is fixed in 38 products on 1 platform, first by DEBIAN-CVE-2026-98401, released October 16, 2026. It is not reported as exploited. Patch Radar priority: High.",
  "title": "net: iptunnel: fix stale transport header during tunnel decapsulation",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  net: iptunnel: fix stale transport header during tunnel decapsulation  Syzbot reported a crash in qdisc_pkt_len_segs_init() caused by a stale transport_header offset after tunnel decapsulation.  BUG: unable to handle page fault for address: ffffed102091a42e Oops: Oops: 0000 [#1] SMP KASAN NOPTI CPU: 0 UID: 0 PID: 340 Comm: qdisc_uaf_repro Not tainted 7.2.0-rc4-00061-g248951ddc14d #256 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 \u002B ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:__asan_load2 \u003CIRQ\u003E qdisc_pkt_len_segs_init (net/core/dev.c:4145) __dev_queue_xmit (net/core/dev.c:4787) br_dev_queue_push_xmit (net/bridge/br_forward.c:53) br_handle_frame_finish (net/bridge/br_input.c:229) br_handle_frame (net/bridge/br_input.c:315) __netif_receive_skb_core.constprop.0 (net/core/dev.c:6099) __netif_receive_skb_list_core (net/core/dev.c:6287) netif_receive_skb_list_internal (net/core/dev.c:6445) napi_complete_done (net/core/dev.c:6813) gro_cell_poll (net/core/gro_cells.c:74) __napi_poll (net/core/dev.c:7735) net_rx_action (net/core/dev.c:7798 net/core/dev.c:7955) handle_softirqs (kernel/softirq.c:622) do_softirq (kernel/softirq.c:523  kernel/softirq.c:510 ) __local_bh_enable_ip (kernel/softirq.c:450) tun_get_user (drivers/net/tun.c:1986 (discriminator 1)) tun_chr_write_iter (drivers/net/tun.c:2032)  The issue is completely latent until qdisc read transport header in commit 7fb4c1967011 (\u0022net: pull headers in qdisc_pkt_len_segs_init()\u0022). The crash requires four conditions to line up:  1. The incoming packet is encapsulated and carries GSO metadata. The outer    transport header offset is stored in skb-\u003Etransport_header while the    packet is still in the outer tunnel context. 2. The tunnel receiver strips the outer headers. skb-\u003Edata is advanced to    the inner frame, but skb-\u003Etransport_header is left pointing to the    now-removed outer L4 header, so it becomes a negative offset relative to    the new data. 3. The inner frame is not delivered to the local IP stack. Instead, it    is forwarded at L2 by a bridge or HSR, so ip_rcv_core() never runs and    the transport header is not reset to the inner L4 offset. 4. The forwarding path calls __dev_queue_xmit(), which enters    qdisc_pkt_len_segs_init(). That function computes the GSO header length    from skb_transport_offset(skb). Because the offset is negative, the    unsigned cast overflows and pskb_may_pull(skb, hdr_len \u002B    sizeof(struct tcphdr)) reads past the end of the skb, triggering a    KASAN fault or page fault.  The issue specifically requires GSO packets (shinfo-\u003Egso_size != 0), which are processed/aggregated through gro_cells. Fix this by clearing transport_header to the ~0U sentinel in gro_cell for all tunnnel driver. GTP does not support GRO/GSO, drop the evil GSO packets in GTP directly.",
  "published": "2026-10-12T09:00:00Z",
  "severity": "Moderate",
  "cvss": 7.5,
  "cvssVector": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
  "epss": 0.00595,
  "epssPercentile": 0.48701,
  "priority": "High",
  "priorityTier": 3,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "vendorAdvisory": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98401",
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