{"id":"CVE-2026-64009","summary":"xfrm: Check for underflow in xfrm_state_mtu","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.","modified":"2026-07-22T03:32:05.545796933Z","published":"2026-07-19T14:56:24.448Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64009.json"},"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"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"c5c2523893747f88a83376abad310c8ad13f7197"},{"fixed":"8014f70c4e6e5ab101ae3860a614e65e988372e3"},{"fixed":"1021d2877b689a648b27815c854557a917122e93"},{"fixed":"2a41b1b31c61c52b972278ce1732a1443f5e89ed"},{"fixed":"fccd685b32df5aaf6bad4381eeda216468e283f0"},{"fixed":"820e501be8aee4b365d218d83227b314309c5fda"},{"fixed":"82ac903e0b519849647657b8c48d21237ada06a2"},{"fixed":"3db50ceeacb52806d8fe86fb1dfe944df0b9f789"},{"fixed":"742b04d0550b0ec89dcbc99537ec88653bd1ad90"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-64009.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","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"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-64009.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}