CVE-2026-80612
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk5th percentile - higher than 5% of all known CVEs
Summary
In the Linux kernel, a vulnerability was found in the LWT (Lightweight Tunnels) mechanism. During LWT encapsulation, skb metadata (passed between XDP and TC) located in the packet headroom is overwritten or cleared, leading to warnings and errors, especially for forwarded packets carrying XDP metadata. The issue affects all LWT encapsulation types (mpls, seg6, ioam6, BPF) and all LWT redirect modes.
Risk Assessment
The vulnerability may cause incorrect packet processing, kernel log warnings, and potential disruption of LWT tunnel operation, impacting network stability and security in environments using XDP/TC and LWT encapsulation.
Recommendation
Apply the kernel patch provided by the Linux vendor as soon as possible, which drops skb metadata before LWT encapsulation. Also monitor kernel logs for skb_data_move warnings and update to a patched kernel version.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: net: lwtunnel: Drop skb metadata before LWT encapsulation skb metadata is meant for passing information between XDP and TC. It lives in the skb headroom, immediately before skb->data. LWT programs cannot access the __sk_buff->data_meta pseudo-pointer to metadata. However, LWT encapsulation prepends outer headers, moving skb->data back over the headroom where the metadata sits. On an RX-originated (forwarded) packet that still carries XDP metadata this goes wrong in two different ways, depending on the encap type: 1. Non-BPF LWT encaps (mpls, seg6, ioam6 ...) call skb_push()/skb_pull() and silently overwrite the metadata that sits in the headroom. 2) BPF LWT xmit calls bpf_skb_change_head(), which uses skb_data_move(). That helper expects metadata immediately before skb->data. But since the IP output path runs LWT xmit before neighbour output has built the outgoing L2 header, for forwarded packets skb->data points at the L3 header while skb_mac_header() still points at the old L2 header. skb_data_move() sees metadata ending at skb_mac_header(), not before skb->data, warns and clears metadata: WARNING: CPU: 21 PID: 454557 at include/linux/skbuff.h:4609 skb_data_move+0x47/0x90 CPU: 21 UID: 0 PID: 454557 Comm: napi/iconduit-g Tainted: G O 6.18.21 #1 RIP: 0010:skb_data_move+0x47/0x90 Call Trace: <IRQ> bpf_skb_change_head+0xe6/0x1a0 bpf_prog_...+0x213/0x2e3 run_lwt_bpf.isra.0+0x1d3/0x360 bpf_xmit+0x46/0xe0 lwtunnel_xmit+0xa1/0xf0 ip_finish_output2+0x1e7/0x5e0 ip_output+0x63/0x100 __netif_receive_skb_one_core+0x85/0xa0 process_backlog+0x9c/0x150 __napi_poll+0x2b/0x190 net_rx_action+0x40b/0x7f0 handle_softirqs+0xd2/0x270 do_softirq+0x3f/0x60 </IRQ> That is what happens, as for how to fix it - a received packet that carries metadata can reach an encap through any of the three LWT redirect modes: LWTUNNEL_STATE_INPUT_REDIRECT ip6_rcv_finish dst_input lwtunnel_input LWTUNNEL_STATE_OUTPUT_REDIRECT ip6_rcv_finish dst_input ip6_forward ip6_forward_finish dst_output lwtunnel_output LWTUNNEL_STATE_XMIT_REDIRECT ip6_rcv_finish dst_input ip6_forward ip6_forward_finish dst_output ip6_output ip6_finish_output ip6_finish_output2 lwtunnel_xmit Every encap funnels through the three LWT dispatch helpers, so drop the metadata there, right before handing the skb to the encap op. This single chokepoint covers all encap types and all three redirect modes: - lwtunnel_input(): seg6, rpl, ila, seg6_local - lwtunnel_output(): ioam6 - lwtunnel_xmit(): mpls, LWT BPF xmit Alternatively, we could clear the metadata right after TC ingress hook. That would require a compromise, however. Metadata would become inaccessible from TC egress (in setups where it actually reaches the hook it tact, that is without any L2 tunnels on path).