CVE-2026-64009

CVE CVE-2026-64009EUVD EUVD-2026-45582Published 2026-07-19T14:56:24.000ZLast changed 2026-08-05T12:38:09.000ZCVSS 7.8

What the advisory describes

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.

Source: EUVD (ENISA), in the words of the advisory.

Products the advisory names

These come from the advisory itself, not from any check we performed.

• Linux — Linux c5c2523893747f88a83376abad310c8ad13f7197 <3db50ceeacb52806d8fe86fb1dfe944df0b9f789; c5c2523893747f88a83376abad310c8ad13f7197 <fccd685b32df5aaf6bad4381eeda216468e283f0; c5c2523893747f88a83376abad310c8ad13f7197 <2a41b1b31c61c52b972278ce1732a1443f5e89ed; c5c2523893747f88a83376abad310c8ad13f7197 <8014f70c4e6e5ab101ae3860a614e65e988372e3; patch: 7.0.12; patch: 5.15.210; patch: 6.18.35; patch: 6.12.93; patch: 6.6.143; patch: 5.10.259; 2.6.22; patch: 7.1; patch: 0; c5c2523893747f88a83376abad310c8ad13f7197 <742b04d0550b0ec89dcbc99537ec88653bd1ad90; c5c2523893747f88a83376abad310c8ad13f7197 <1021d2877b689a648b27815c854557a917122e93; patch: 6.1.176; c5c2523893747f88a83376abad310c8ad13f7197 <820e501be8aee4b365d218d83227b314309c5fda; c5c2523893747f88a83376abad310c8ad13f7197 <82ac903e0b519849647657b8c48d21237ada06a2

The versions shown are the advisory's own. Patchlage compares no version numbers and derives no judgement from them — which version is installed is something a person has to look up.

Carried in the product catalogue

An estate covering these products can be recorded in Patchlage. An advisory about them appears in the next morning's situation report.

• Linux — Linux

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