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CVE-2026-64009

xfrm: Check for underflow in xfrm_state_mtu

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.93, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: no
  • Technical impact: total

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.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: no · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From c5c2523893747f88a83376abad310c8ad13f7197 · fixed in 8014f70c4e6e5ab101ae3860a614e65e988372e3; From c5c2523893747f88a83376abad310c8ad13f7197 · fixed in 1021d2877b689a648b27815c854557a917122e93; From c5c2523893747f88a83376abad310c8ad13f7197 · fixed in 2a41b1b31c61c52b972278ce1732a1443f5e89ed; From c5c2523893747f88a83376abad310c8ad13f7197 · fixed in fccd685b32df5aaf6bad4381eeda216468e283f0; From c5c2523893747f88a83376abad310c8ad13f7197 · fixed in 820e501be8aee4b365d218d83227b314309c5fda; From c5c2523893747f88a83376abad310c8ad13f7197 · fixed in 82ac903e0b519849647657b8c48d21237ada06a2; From c5c2523893747f88a83376abad310c8ad13f7197 · fixed in 3db50ceeacb52806d8fe86fb1dfe944df0b9f789; From c5c2523893747f88a83376abad310c8ad13f7197 · fixed in 742b04d0550b0ec89dcbc99537ec88653bd1ad90

  • Linux Linux

    2.6.22

  • KernelLinux

    From 2.6.22 · fixed in 5.10.259; From 5.11.0 · fixed in 5.15.210; From 5.16.0 · fixed in 6.1.176; From 6.2.0 · fixed in 6.6.143; From 6.7.0 · fixed in 6.12.93; From 6.13.0 · fixed in 6.18.35; From 6.19.0 · fixed in 7.0.12

References 8

git.kernel.org