GHSA-666Q-FGC6-3X4W

Vulnerability from github – Published: 2026-07-19 18:31 – Updated: 2026-07-20 15:31
VLAI
Details

In the Linux kernel, the following vulnerability has been resolved:

xfrm: Check for underflow in xfrm_state_mtu

Leo Lin reported OOB write issue in esp component:

xfrm_state_mtu() returns u32 but performs its arithmetic in unsigned modulo-2^32 space using an attacker-influenced "header_len + authsize + net_adj" subtracted from a small "mtu" argument. A nobody user can install an IPv4 ESP tunnel SA with a large authentication key (XFRMA_ALG_AUTH_TRUNC, e.g. hmac(sha512), 64-byte key, 64-byte trunc), configure a small interface MTU (68 bytes), and set XFRMA_TFCPAD to a large value. When a single UDP datagram is then sent through the tunnel, xfrm_state_mtu() underflows to a near-2^32 value, and esp_output() consumes it as a signed int via:

    padto      = min(x->tfcpad, xfrm_state_mtu(x, mtu_cached))
    esp.tfclen = padto - skb->len   (assigned to int)

esp.tfclen ends up negative (e.g. -207). It is sign-extended to size_t when passed to memset() inside esp_output_fill_trailer(), producing a ~16 EB write of zeroes at skb_tail_pointer(skb). KASAN logs it as "Write of size 18446744073709551537 at addr ffff888...".

Check for underflow and return 1. This causes the sendmsg attempt to fail with ENETUNREACH.

Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-64009"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-19T16:17:40Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nxfrm: Check for underflow in xfrm_state_mtu\n\nLeo Lin reported OOB write issue in esp component:\n\n  xfrm_state_mtu() returns u32 but performs its arithmetic in unsigned\n  modulo-2^32 space using an attacker-influenced \"header_len + authsize +\n  net_adj\" subtracted from a small \"mtu\" argument. A nobody user can\n  install an IPv4 ESP tunnel SA with a large authentication key\n  (XFRMA_ALG_AUTH_TRUNC, e.g. hmac(sha512), 64-byte key, 64-byte trunc),\n  configure a small interface MTU (68 bytes), and set XFRMA_TFCPAD to a\n  large value. When a single UDP datagram is then sent through the\n  tunnel, xfrm_state_mtu() underflows to a near-2^32 value, and\n  esp_output() consumes it as a signed int via:\n\n        padto      = min(x-\u003etfcpad, xfrm_state_mtu(x, mtu_cached))\n        esp.tfclen = padto - skb-\u003elen   (assigned to int)\n\n  esp.tfclen ends up negative (e.g. -207). It is sign-extended to size_t\n  when passed to memset() inside esp_output_fill_trailer(), producing a\n  ~16 EB write of zeroes at skb_tail_pointer(skb). KASAN logs it as\n  \"Write of size 18446744073709551537 at addr ffff888...\".\n\nCheck for underflow and return 1. This causes the sendmsg attempt to\nfail with ENETUNREACH.",
  "id": "GHSA-666q-fgc6-3x4w",
  "modified": "2026-07-20T15:31:55Z",
  "published": "2026-07-19T18:31:49Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64009"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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