CVE-2026-74478

Summary

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

um: vector: fix use-after-free in vector_mmsg_rx()

When vector_mmsg_rx() discards a packet whose overlay header fails verify_header(), it frees the skb and continues the loop:

if (header_check < 0) {
	dev_kfree_skb_irq(skb);
	vp->estats.rx_encaps_errors++;
	continue;
}

The normal and short-packet paths fall through to the bottom of the loop body, which clears the consumed slot and advances the cursors:

(*skbuff_vector) = NULL;
mmsg_vector++;
skbuff_vector++;

The verify_header() < 0 path skips that via continue, so the freed skb is left in skbuff_vector[] and the cursors do not advance. The next iteration reads the same slot, gets the freed skb, and frees it again, producing a refcount underflow / use-after-free in the RX path.

Discard the slot the same way the other paths do before continuing.

Only transports whose verify_header() can return negative are affected: GRE and L2TPv3 do so on a cookie/session-id mismatch (raw/tap do not), so any peer on such a transport can trigger it without authentication.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/4b9601595e8b6b5d18878cac0aeabc687d241111
• https://git.kernel.org/stable/c/67d58ab4f2ccf7145f3da07e025735a09c79de1b
• https://git.kernel.org/stable/c/180ff4c81faf01ec4e06082c9daa7c40518ead89
• https://git.kernel.org/stable/c/804b681002ead233abf49a3efd681f5468a835f9
• https://git.kernel.org/stable/c/af421e9aed3920c7ac88c24daa48606c7112feca

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