CVE-2026-64009xfrm: Check for underflow in xfrm_state_mtu
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 7.8 HIGH (v3.1, CNA)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Weakness (CWE)
- Not given
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Linux
- NVD analysis
- Analyzed
- Record last updated
- Oct 16, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Linux Linux linux:linux (from the name) | from c5c2523893747f88a83376abad310c8ad13f7197 before 8014f70c4e6e5ab101ae3860a614e65e988372e3; from c5c2523893747f88a83376abad310c8ad13f7197 before 1021d2877b689a648b27815c854557a917122e93; from c5c2523893747f88a83376abad310c8ad13f7197 before 2a41b1b31c61c52b972278ce1732a1443f5e89ed; from c5c2523893747f88a83376abad310c8ad13f7197 before fccd685b32df5aaf6bad4381eeda216468e283f0; from c5c2523893747f88a83376abad310c8ad13f7197 before 820e501be8aee4b365d218d83227b314309c5fda; from c5c2523893747f88a83376abad310c8ad13f7197 before 82ac903e0b519849647657b8c48d21237ada06a2; from c5c2523893747f88a83376abad310c8ad13f7197 before 3db50ceeacb52806d8fe86fb1dfe944df0b9f789; from c5c2523893747f88a83376abad310c8ad13f7197 before 742b04d0550b0ec89dcbc99537ec88653bd1ad90 | CNA record |
linux linux_kernel linux:linux_kernel | from 2.6.22 before 5.10.259; from 5.11 before 5.15.210; from 5.16 before 6.1.176; from 6.2 before 6.6.143; from 6.7 before 6.12.93; from 6.13 before 6.18.35; from 6.19 before 7.0.12; 7.1; and 4 more ranges | NVD |
References
- https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3patch
- https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93patch
- https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89edpatch
- https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0patch
- https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fdapatch
- https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2patch
- https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789patch
- https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90patch
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.