{"api_version":"1","generated_at":"2026-07-22T12:30:43+00:00","cve":"CVE-2026-64009","urls":{"html":"https://cve.report/CVE-2026-64009","api":"https://cve.report/api/cve/CVE-2026-64009.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-64009","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-64009"},"summary":{"title":"xfrm: Check for underflow in xfrm_state_mtu","description":"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->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.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-07-19 16:17:40","updated_at":"2026-07-20 15:17:02"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"baseScore":7.8,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"references":[{"url":"https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789","name":"https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93","name":"https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90","name":"https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2","name":"https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3","name":"https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed","name":"https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0","name":"https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda","name":"https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-64009","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64009","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected c5c2523893747f88a83376abad310c8ad13f7197 8014f70c4e6e5ab101ae3860a614e65e988372e3 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected c5c2523893747f88a83376abad310c8ad13f7197 1021d2877b689a648b27815c854557a917122e93 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected c5c2523893747f88a83376abad310c8ad13f7197 2a41b1b31c61c52b972278ce1732a1443f5e89ed git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected c5c2523893747f88a83376abad310c8ad13f7197 fccd685b32df5aaf6bad4381eeda216468e283f0 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 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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."}],"metrics":[{"cvssV3_1":{"baseScore":7.8,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"providerMetadata":{"dateUpdated":"2026-07-20T13:42:19.937Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3"},{"url":"https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93"},{"url":"https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed"},{"url":"https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0"},{"url":"https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda"},{"url":"https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2"},{"url":"https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789"},{"url":"https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90"}],"title":"xfrm: Check for underflow in xfrm_state_mtu","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-64009","datePublished":"2026-07-19T14:56:24.448Z","dateReserved":"2026-07-19T07:54:57.026Z","dateUpdated":"2026-07-20T13:42:19.937Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-07-19 16:17:40","lastModifiedDate":"2026-07-20 15:17:02","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":5.9}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"64009","Ordinal":"1","Title":"xfrm: Check for underflow in xfrm_state_mtu","CVE":"CVE-2026-64009","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"64009","Ordinal":"1","NoteData":"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->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.","Type":"Description","Title":"xfrm: Check for underflow in xfrm_state_mtu"}]}}}