CVE-2026-64009High· 7.8▾ TwilightIn 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 …
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 42.9 · likelihood 0 · exploitation 0
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Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
Last analysed / modified upstream
0.2%
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.
linux_kernel >= 2.6.22, < 5.10.259linux_kernel >= 5.11, < 5.15.210linux_kernel >= 5.16, < 6.1.176linux_kernel >= 6.2, < 6.6.143linux_kernel >= 6.7, < 6.12.93linux_kernel >= 6.13, < 6.18.35linux_kernel >= 6.19, < 7.0.12linux_kernel = 7.1Upgrade past the affected range:
linux_kernel 7.0.12Connected by shared product, vendor, weakness, or advisory.
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