{"id":"CVE-2026-64009","title":"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…","summary":"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…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cwe":["CWE-787"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 2.6.22, < 5.10.259","linux_kernel >= 5.11, < 5.15.210","linux_kernel >= 5.16, < 6.1.176","linux_kernel >= 6.2, < 6.6.143","linux_kernel >= 6.7, < 6.12.93","linux_kernel >= 6.13, < 6.18.35","linux_kernel >= 6.19, < 7.0.12","linux_kernel = 7.1"],"patched":["linux_kernel 7.0.12"],"published":"2026-07-19","updated":"2026-10-13","sourceUpdated":"2026-10-13T13:59:46.923","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-64009","references":[{"url":"https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd"],"epss":0.00201,"epssPercentile":0.09247,"ingestedAt":"2026-10-13T14:29:01.773Z","slug":"CVE-2026-64009","body":"## Overview\n\nIn 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->tfcpad, xfrm_state_mtu(x, mtu_cached))\n        esp.tfclen = padto - skb->len   (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.\n\n## Affected\n\n- `linux_kernel >= 2.6.22, < 5.10.259`\n- `linux_kernel >= 5.11, < 5.15.210`\n- `linux_kernel >= 5.16, < 6.1.176`\n- `linux_kernel >= 6.2, < 6.6.143`\n- `linux_kernel >= 6.7, < 6.12.93`\n- `linux_kernel >= 6.13, < 6.18.35`\n- `linux_kernel >= 6.19, < 7.0.12`\n- `linux_kernel = 7.1`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 7.0.12`","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}