Tracker / CVE-2026-64009
CVE-2026-64009
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.
Affected products and versions
| linux | linux_kernel |
|---|---|
| linux | linux_kernel · 2.6.22 → 5.10.259 |
| linux | linux_kernel · 5.11 → 5.15.210 |
| linux | linux_kernel · 5.16 → 6.1.176 |
| linux | linux_kernel · 6.13 → 6.18.35 |
| linux | linux_kernel · 6.19 → 7.0.12 |
| linux | linux_kernel · 6.2 → 6.6.143 |
| linux | linux_kernel · 6.7 → 6.12.93 |