CVE-2026-98401 (GCVE-0-2026-98401)
Vulnerability from cvelistv5
Published
2026-10-14 13:26
Modified
2026-10-24 14:08
Severity ?
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Summary
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 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:__asan_load2 <IRQ> 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 ("net: pull headers in qdisc_pkt_len_segs_init()"). 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->transport_header while the packet is still in the outer tunnel context. 2. The tunnel receiver strips the outer headers. skb->data is advanced to the inner frame, but skb->transport_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 + sizeof(struct tcphdr)) reads past the end of the skb, triggering a KASAN fault or page fault. The issue specifically requires GSO packets (shinfo->gso_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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/gtp.c",
            "include/linux/skbuff.h",
            "net/core/gro_cells.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "8c3d4dfcecf7670c1d752f1ae74b21b2af5feac1",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            },
            {
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              "versionType": "git"
            },
            {
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              "status": "affected",
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              "versionType": "git"
            },
            {
              "lessThan": "28a57fb2c5df4deb42a06e52fd36c14b37aa0034",
              "status": "affected",
              "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/gtp.c",
            "include/linux/skbuff.h",
            "net/core/gro_cells.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.12"
            },
            {
              "lessThan": "2.6.12",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.111",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.53",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.7",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.111",
                  "versionStartIncluding": "2.6.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.53",
                  "versionStartIncluding": "2.6.12",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.7",
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                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "2.6.12",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: iptunnel: fix stale transport header during tunnel decapsulation\n\nSyzbot reported a crash in qdisc_pkt_len_segs_init() caused by a stale\ntransport_header offset after tunnel decapsulation.\n\nBUG: unable to handle page fault for address: ffffed102091a42e\nOops: Oops: 0000 [#1] SMP KASAN NOPTI\nCPU: 0 UID: 0 PID: 340 Comm: qdisc_uaf_repro Not tainted 7.2.0-rc4-00061-g248951ddc14d #256 PREEMPT(full)\nHardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014\nRIP: 0010:__asan_load2\n\u003cIRQ\u003e\nqdisc_pkt_len_segs_init (net/core/dev.c:4145)\n__dev_queue_xmit (net/core/dev.c:4787)\nbr_dev_queue_push_xmit (net/bridge/br_forward.c:53)\nbr_handle_frame_finish (net/bridge/br_input.c:229)\nbr_handle_frame (net/bridge/br_input.c:315)\n__netif_receive_skb_core.constprop.0 (net/core/dev.c:6099)\n__netif_receive_skb_list_core (net/core/dev.c:6287)\nnetif_receive_skb_list_internal (net/core/dev.c:6445)\nnapi_complete_done (net/core/dev.c:6813)\ngro_cell_poll (net/core/gro_cells.c:74)\n__napi_poll (net/core/dev.c:7735)\nnet_rx_action (net/core/dev.c:7798 net/core/dev.c:7955)\nhandle_softirqs (kernel/softirq.c:622)\ndo_softirq (kernel/softirq.c:523  kernel/softirq.c:510 )\n__local_bh_enable_ip (kernel/softirq.c:450)\ntun_get_user (drivers/net/tun.c:1986 (discriminator 1))\ntun_chr_write_iter (drivers/net/tun.c:2032)\n\nThe issue is completely latent until qdisc read transport header in\ncommit 7fb4c1967011 (\"net: pull headers in qdisc_pkt_len_segs_init()\").\nThe crash requires four conditions to line up:\n\n1. The incoming packet is encapsulated and carries GSO metadata. The outer\n   transport header offset is stored in skb-\u003etransport_header while the\n   packet is still in the outer tunnel context.\n2. The tunnel receiver strips the outer headers. skb-\u003edata is advanced to\n   the inner frame, but skb-\u003etransport_header is left pointing to the\n   now-removed outer L4 header, so it becomes a negative offset relative to\n   the new data.\n3. The inner frame is not delivered to the local IP stack. Instead, it\n   is forwarded at L2 by a bridge or HSR, so ip_rcv_core() never runs and\n   the transport header is not reset to the inner L4 offset.\n4. The forwarding path calls __dev_queue_xmit(), which enters\n   qdisc_pkt_len_segs_init(). That function computes the GSO header length\n   from skb_transport_offset(skb). Because the offset is negative, the\n   unsigned cast overflows and pskb_may_pull(skb, hdr_len +\n   sizeof(struct tcphdr)) reads past the end of the skb, triggering a\n   KASAN fault or page fault.\n\nThe issue specifically requires GSO packets (shinfo-\u003egso_size != 0), which\nare processed/aggregated through gro_cells. Fix this by clearing\ntransport_header to the ~0U sentinel in gro_cell for all tunnnel driver.\nGTP does not support GRO/GSO, drop the evil GSO packets in GTP directly."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - An unauthenticated peer can send IPv4/IPv6 GRE packets carrying inner TCP frames; gre_gro_receive() creates the GSO skb, and gre_rcv() through ip6_tnl_rcv() reaches the patched gro_cells_receive() before bridge forwarding invokes qdisc_pkt_len_segs_init().\nAC:L - On a bridged GRETAP endpoint, the attacker sends same-flow GRE-encapsulated TCP segments to induce GRO and chooses a nonlocal inner destination so br_handle_frame_finish() forwards them. These packet conditions are attacker-controlled and require no race.\nPR:N - ip6_input_finish() dispatches protocol 47 to gre_rcv(), where ip6gre_tunnel_lookup() selects the configured tunnel without authenticating the sender or checking task credentials. No target-system privilege is required once the GRETAP endpoint is running.\nUI:N - The received GRE stream automatically traverses GRO, gre_rcv(), gro_cells_receive(), and bridge egress; no victim must open data, approve a request, or perform another action.\nS:U - qdisc_pkt_len_segs_init() dereferences the invalid skb header pointer inside the host kernel\u0027s receive and forwarding paths. The resulting fault does not cross a VM, IOMMU, or other security-authority boundary.\nC:N - After basic GRE decapsulation and bridge Ethernet-header restoration, the stale transport offset is -4; unsigned wrap makes __tcp_hdrlen() perform a two-byte invalid read, but the value is only used for header-length and drop accounting and is never copied or returned to the peer.\nI:N - __tcp_hdrlen() only reads th-\u003edoff through the invalid pointer; subsequent code drops the skb or updates its qdisc length metadata. The code provides no write primitive or demonstrated modification of protected kernel or user data.\nA:H - The out-of-bounds th-\u003edoff load in qdisc_pkt_len_segs_init() can fault roughly 4 GiB beyond skb-\u003edata. The observed bridge-forwarding path produces a KASAN or page-fault Oops and can be triggered repeatedly with packet streams."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-24T14:08:43.092Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/8c3d4dfcecf7670c1d752f1ae74b21b2af5feac1"
        },
        {
          "url": "https://git.kernel.org/stable/c/e4a5b01e59f7102169762b8f566c8e052d05c0ff"
        },
        {
          "url": "https://git.kernel.org/stable/c/3340b8565b85631cfeb0df049e8b46e3ef8bd7bd"
        },
        {
          "url": "https://git.kernel.org/stable/c/28a57fb2c5df4deb42a06e52fd36c14b37aa0034"
        }
      ],
      "title": "net: iptunnel: fix stale transport header during tunnel decapsulation",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98401",
    "datePublished": "2026-10-14T13:26:01.712Z",
    "dateReserved": "2026-09-25T10:25:14.346Z",
    "dateUpdated": "2026-10-24T14:08:43.092Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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