CVE-2026-64009 (GCVE-0-2026-64009)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:56 – Updated: 2026-10-19 20:28
VLAI
Title
xfrm: Check for underflow in xfrm_state_mtu
Summary
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
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-16 15:35 UTC
CWE
  • CWE-191 - Integer Underflow (Wrap or Wraparound)
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6996 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: c5c2523893747f88a83376abad310c8ad13f7197 , < 8014f70c4e6e5ab101ae3860a614e65e988372e3 (git)
Affected: c5c2523893747f88a83376abad310c8ad13f7197 , < 1021d2877b689a648b27815c854557a917122e93 (git)
Affected: c5c2523893747f88a83376abad310c8ad13f7197 , < 2a41b1b31c61c52b972278ce1732a1443f5e89ed (git)
Affected: c5c2523893747f88a83376abad310c8ad13f7197 , < fccd685b32df5aaf6bad4381eeda216468e283f0 (git)
Affected: c5c2523893747f88a83376abad310c8ad13f7197 , < 820e501be8aee4b365d218d83227b314309c5fda (git)
Affected: c5c2523893747f88a83376abad310c8ad13f7197 , < 82ac903e0b519849647657b8c48d21237ada06a2 (git)
Affected: c5c2523893747f88a83376abad310c8ad13f7197 , < 3db50ceeacb52806d8fe86fb1dfe944df0b9f789 (git)
Affected: c5c2523893747f88a83376abad310c8ad13f7197 , < 742b04d0550b0ec89dcbc99537ec88653bd1ad90 (git)
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Linux Linux Affected: 2.6.22
Unaffected: 0 , < 2.6.22 (semver)
Unaffected: 5.10.259 , ≤ 5.10.* (semver)
Unaffected: 5.15.210 , ≤ 5.15.* (semver)
Unaffected: 6.1.176 , ≤ 6.1.* (semver)
Unaffected: 6.6.143 , ≤ 6.6.* (semver)
Unaffected: 6.12.93 , ≤ 6.12.* (semver)
Unaffected: 6.18.35 , ≤ 6.18.* (semver)
Unaffected: 7.0.12 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
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            "value": "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."
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      "product_status:known_affected": "261",
      "product_status:under_investigation": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: xfrm: Check for underflow in xfrm_state_mtu",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64009.json",
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}



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