CVE-2026-74478
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk10th percentile - higher than 10% of all known CVEs
Summary
In the Linux kernel, the UML vector driver has a use-after-free bug in vector_mmsg_rx() when a packet with an invalid header is discarded. The freed skb remains in the buffer, leading to double-free and potential exploitation.
Risk Assessment
A remote attacker sending specially crafted GRE or L2TPv3 packets could cause a system crash or gain unauthorized access to kernel memory.
Recommendation
Apply the Linux kernel patch that clears the buffer slot before continuing the loop to avoid double-free.
Original NVD description (English source)
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.