CVE-2026-98955 (GCVE-0-2026-98955)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:19 – Updated: 2026-10-23 12:19
VLAI
Title
flow_dissector: avoid u16 truncation of skb->len when computing thoff
Summary
In the Linux kernel, the following vulnerability has been resolved: flow_dissector: avoid u16 truncation of skb->len when computing thoff __skb_flow_dissect() computes key_control->thoff using: key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen); min_t(u16, ...) casts both arguments to u16 before comparing them. Whenever skb->len (or hlen) modulo 65536 is smaller than nhoff, the truncated length wins and thoff is set to a bogus small value, even when the dissection succeeded. For example, an IPv4/TCP frame with skb->len == 65540 and nhoff == 34 gets thoff == 4, so callers such as skb_probe_transport_header() point the transport header inside the Ethernet header. Such skbs are not exotic: - At the time of commit d0c081b49137 ("flow_dissector: properly cap thoff field"), AF_PACKET with PACKET_VNET_HDR could already build GSO skbs larger than 64KB (MTU checks are skipped for GSO, and alloc_skb_with_frags() accepted up to MAX_SKB_FRAGS (17) order-0 pages on top of the linear part). - BIG TCP now makes skbs larger than 64KB common. - The following patch makes tun_get_user() dissect IFF_TAP frames before eth_type_trans() pulls the Ethernet header, so a GSO frame carrying a 65522..65535 byte L3 packet will be dissected with skb->len in [65536, 65549]. Compare as u32 instead. If the resulting offset cannot be represented in the u16 key_control->thoff, cap it to U16_MAX and report the dissection as failed rather than silently returning a wrong transport offset. thoff is still set on failure, as some callers (such as eth_get_headlen()) use it regardless of the return value.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7063 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: d0c081b49137cd3200f2023c0875723be66e7ce5 , < d9e08836d06c84abb18470c94b12b131eaccdc7d (git)
Affected: d0c081b49137cd3200f2023c0875723be66e7ce5 , < 50d0cd575cab763f833d6ac6eb6550b23a0b3dae (git)
Affected: d0c081b49137cd3200f2023c0875723be66e7ce5 , < 9993e6a0ac1b5b3101ffba702cacb9f42b9909d8 (git)
Affected: d0c081b49137cd3200f2023c0875723be66e7ce5 , < 52efce4755a4b8b82039caa773645ffc80b25362 (git)
Affected: d0c081b49137cd3200f2023c0875723be66e7ce5 , < 99bda1ecbd56905f8bd934b9cdccd3bd251192b1 (git)
Affected: d35cd5e279881ec36ff8cd82a2d9caebc0cce3fc (git)
Affected: eecfa2eeefe3caef4c8d6b2284f6066c76ab26a1 (git)
Affected: 80f327285cab6ab8e10c3ea03278add5dd99fb02 (git)
Affected: 4.4.114 , < 4.5 (semver)
Affected: 4.9.79 , < 4.10 (semver)
Affected: 4.14.16 , < 4.15 (semver)
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Linux Linux Affected: 4.15
Unaffected: 0 , < 4.15 (semver)
Unaffected: 6.6.160 , ≤ 6.6.* (semver)
Unaffected: 6.12.113 , ≤ 6.12.* (semver)
Unaffected: 6.18.57 , ≤ 6.18.* (semver)
Unaffected: 7.2.11 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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{
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          "product": "Linux",
          "programFiles": [
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              "version": "7.3",
              "versionType": "original_commit_for_fix"
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      ],
      "cpeApplicability": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nflow_dissector: avoid u16 truncation of skb-\u003elen when computing thoff\n\n__skb_flow_dissect() computes key_control-\u003ethoff using:\n\n  key_control-\u003ethoff = min_t(u16, nhoff, skb ? skb-\u003elen : hlen);\n\nmin_t(u16, ...) casts both arguments to u16 before comparing them.\nWhenever skb-\u003elen (or hlen) modulo 65536 is smaller than nhoff, the\ntruncated length wins and thoff is set to a bogus small value, even\nwhen the dissection succeeded. For example, an IPv4/TCP frame with\nskb-\u003elen == 65540 and nhoff == 34 gets thoff == 4, so callers such as\nskb_probe_transport_header() point the transport header inside the\nEthernet header.\n\nSuch skbs are not exotic:\n- At the time of commit d0c081b49137 (\"flow_dissector: properly cap\n  thoff field\"), AF_PACKET with PACKET_VNET_HDR could already build GSO\n  skbs larger than 64KB (MTU checks are skipped for GSO, and\n  alloc_skb_with_frags() accepted up to MAX_SKB_FRAGS (17) order-0\n  pages on top of the linear part).\n- BIG TCP now makes skbs larger than 64KB common.\n- The following patch makes tun_get_user() dissect IFF_TAP frames\n  before eth_type_trans() pulls the Ethernet header, so a GSO frame\n  carrying a 65522..65535 byte L3 packet will be dissected with\n  skb-\u003elen in [65536, 65549].\n\nCompare as u32 instead. If the resulting offset cannot be represented\nin the u16 key_control-\u003ethoff, cap it to U16_MAX and report the\ndissection as failed rather than silently returning a wrong transport\noffset. thoff is still set on failure, as some callers (such as\neth_get_headlen()) use it regardless of the return value."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-23T12:19:15.287Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/d9e08836d06c84abb18470c94b12b131eaccdc7d"
        },
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          "url": "https://git.kernel.org/stable/c/50d0cd575cab763f833d6ac6eb6550b23a0b3dae"
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        },
        {
          "url": "https://git.kernel.org/stable/c/52efce4755a4b8b82039caa773645ffc80b25362"
        },
        {
          "url": "https://git.kernel.org/stable/c/99bda1ecbd56905f8bd934b9cdccd3bd251192b1"
        }
      ],
      "title": "flow_dissector: avoid u16 truncation of skb-\u003elen when computing thoff",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98955",
    "datePublished": "2026-10-23T12:19:15.287Z",
    "dateReserved": "2026-09-25T10:25:14.382Z",
    "dateUpdated": "2026-10-23T12:19:15.287Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "cve": "CVE-2026-98955",
      "date": "2026-10-27",
      "epss": "0.00168",
      "percentile": "0.06155"
    },
    "microsoft_vex": {
      "current_release_date": "2026-10-26T14:47:49.000Z",
      "cve": "CVE-2026-98955",
      "id": "msrc_CVE-2026-98955",
      "initial_release_date": "2026-10-24T01:09:40.000Z",
      "product_status:known_affected": "1",
      "product_status:under_investigation": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "flow_dissector: avoid u16 truncation of skb-\u003elen when computing thoff",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-98955.json",
      "version": "3"
    },
    "nvd": {
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nflow_dissector: avoid u16 truncation of skb-\u003elen when computing thoff\n\n__skb_flow_dissect() computes key_control-\u003ethoff using:\n\n  key_control-\u003ethoff = min_t(u16, nhoff, skb ? skb-\u003elen : hlen);\n\nmin_t(u16, ...) casts both arguments to u16 before comparing them.\nWhenever skb-\u003elen (or hlen) modulo 65536 is smaller than nhoff, the\ntruncated length wins and thoff is set to a bogus small value, even\nwhen the dissection succeeded. For example, an IPv4/TCP frame with\nskb-\u003elen == 65540 and nhoff == 34 gets thoff == 4, so callers such as\nskb_probe_transport_header() point the transport header inside the\nEthernet header.\n\nSuch skbs are not exotic:\n- At the time of commit d0c081b49137 (\"flow_dissector: properly cap\n  thoff field\"), AF_PACKET with PACKET_VNET_HDR could already build GSO\n  skbs larger than 64KB (MTU checks are skipped for GSO, and\n  alloc_skb_with_frags() accepted up to MAX_SKB_FRAGS (17) order-0\n  pages on top of the linear part).\n- BIG TCP now makes skbs larger than 64KB common.\n- The following patch makes tun_get_user() dissect IFF_TAP frames\n  before eth_type_trans() pulls the Ethernet header, so a GSO frame\n  carrying a 65522..65535 byte L3 packet will be dissected with\n  skb-\u003elen in [65536, 65549].\n\nCompare as u32 instead. If the resulting offset cannot be represented\nin the u16 key_control-\u003ethoff, cap it to U16_MAX and report the\ndissection as failed rather than silently returning a wrong transport\noffset. thoff is still set on failure, as some callers (such as\neth_get_headlen()) use it regardless of the return value."
          }
        ],
        "id": "CVE-2026-98955",
        "lastModified": "2026-10-23T13:17:16.740",
        "metrics": {},
        "published": "2026-10-23T13:17:16.740",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/50d0cd575cab763f833d6ac6eb6550b23a0b3dae"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/9993e6a0ac1b5b3101ffba702cacb9f42b9909d8"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/99bda1ecbd56905f8bd934b9cdccd3bd251192b1"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/d9e08836d06c84abb18470c94b12b131eaccdc7d"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    }
  }
}



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