CVE-2026-64114

Summary

In the Linux kernel, the following vulnerability has been resolved:

ipv4: raw: reject IP_HDRINCL packets with ihl < 5

raw_send_hdrinc() validates that the caller-supplied IPv4 header fits within the message length:

iphlen = iph->ihl * 4;
err = -EINVAL;
if (iphlen > length)
    goto error_free;

if (iphlen >= sizeof(*iph)) {
    /* fix up saddr, tot_len, id, csum, transport_header */
}

It does not, however, reject ihl < 5. For such a packet the "if (iphlen >= sizeof(*iph))" branch is skipped, leaving the crafted iphdr untouched, but the packet is still handed to __ip_local_out() and onward. Downstream consumers that read iph->ihl assume a sane value: net/ipv4/ah4.c:ah_output() in particular subtracts sizeof(struct iphdr) from top_iph->ihl * 4 and passes the (signed-int-negative, then cast to size_t) result to memcpy(), producing an OOB access of length close to SIZE_MAX and a host kernel panic.

An IPv4 header with ihl < 5 is malformed by definition (RFC 791: "Internet Header Length is the length of the internet header in 32 bit words … Note that the minimum value for a correct header is 5."). The kernel should not be willing to inject such a packet into its own output path.

Reject "iphlen < sizeof(*iph)" alongside the existing "iphlen > length" check. This matches the principle that locally constructed packets that re-enter the IP stack must pass the same basic sanity tests that a foreign packet would be subjected to.

Once this lands, the "if (iphlen >= sizeof(*iph))" wrapper around the fixup branch becomes redundant; left in place to keep the patch minimal and backport-friendly. A follow-up can unwrap it.

Note that commit 86f4c90a1c5c ("ipv4, ipv6: ensure raw socket message is big enough to hold an IP header") ensures the message buffer is large enough to hold an iphdr, but does not constrain the self-reported iph->ihl.

Reachability: the malformed packet source is any caller with CAP_NET_RAW, including an unprivileged process in a user+net namespace on a kernel with CONFIG_USER_NS=y. The reproduced AH crash also requires a matching xfrm AH policy on the outgoing route; a container granted CAP_NET_ADMIN can install that state and policy in its netns. Loopback bypasses xfrm_output, so the trigger uses a real netdev.

Reproduced on UML + KASAN: kernel-mode fault at addr 0x0 with memcpy_orig at the crash site. Same shape reproduces inside a rootless Docker container with –cap-add NET_ADMIN on a stock distro kernel.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/1065b9efa4126df559b03a849c139ecfae92cd25
• https://git.kernel.org/stable/c/bc20dbd48c26e743f7e0845020c11ed2ce8b15ee
• https://git.kernel.org/stable/c/5a564f737ec54d63e8ee221d3ff396d07586d464
• https://git.kernel.org/stable/c/3c5411fa4944ed99af3d9d1de750ea8169b6dac9
• https://git.kernel.org/stable/c/145e9afa5b905229b4788bb72c3255f5a5f77508
• https://git.kernel.org/stable/c/7725cd3b471740fd23d25ed1da722c671fb2a5d3
• https://git.kernel.org/stable/c/bbe0be67de296176e7243c76e3d9f02f6ae9ff0b
• https://git.kernel.org/stable/c/915fab69823a14c170dbaa3b41978768e0fe62fc

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