{
  "affected": [
    {
      "ranges": [
        {
          "events": [
            {
              "introduced": "c5c2523893747f88a83376abad310c8ad13f7197"
            },
            {
              "fixed": "8014f70c4e6e5ab101ae3860a614e65e988372e3"
            },
            {
              "fixed": "1021d2877b689a648b27815c854557a917122e93"
            },
            {
              "fixed": "2a41b1b31c61c52b972278ce1732a1443f5e89ed"
            },
            {
              "fixed": "fccd685b32df5aaf6bad4381eeda216468e283f0"
            },
            {
              "fixed": "820e501be8aee4b365d218d83227b314309c5fda"
            },
            {
              "fixed": "82ac903e0b519849647657b8c48d21237ada06a2"
            },
            {
              "fixed": "3db50ceeacb52806d8fe86fb1dfe944df0b9f789"
            },
            {
              "fixed": "742b04d0550b0ec89dcbc99537ec88653bd1ad90"
            }
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "type": "GIT"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Linux",
        "name": "Kernel"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.6.22"
            },
            {
              "fixed": "5.10.259"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "5.11.0"
            },
            {
              "fixed": "5.15.210"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "5.16.0"
            },
            {
              "fixed": "6.1.176"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.2.0"
            },
            {
              "fixed": "6.6.143"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.7.0"
            },
            {
              "fixed": "6.12.93"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.13.0"
            },
            {
              "fixed": "6.18.35"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.19.0"
            },
            {
              "fixed": "7.0.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "Linux",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64009.json"
  },
  "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": "CVE-2026-64009",
  "modified": "2026-07-22T05:29:50.565056719Z",
  "published": "2026-07-19T14:56:24.448Z",
  "references": [
    {
      "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"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64009.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64009"
    },
    {
      "type": "PACKAGE",
      "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "xfrm: Check for underflow in xfrm_state_mtu"
}