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CVE-2026-80612
net: lwtunnel: Drop skb metadata before LWT encapsulation
Published 2026-08-28 (2 months ago) by the Linux kernel CNA. Subsystem net/core. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-80612 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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).
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/core/lwtunnel.c
- What this is
- NETWORKING [IPv4/IPv6]MAINTAINERS section matched on net/core/lwtunnel.c · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_LWTUNNEL /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_LWTUNNEL
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-28 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.55%, higher than 45.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/core
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.19 | 7.1.5 | 19eec11f3ab5 |
| 6.19 | 7.2 | c00320b0e355 |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- The bug fires on the network RX datapath in softirq when remotely sourced packets are received, forwarded, and LWT-encapsulated (ip6_rcv_finish to ip6_forward to lwtunnel_xmit as shown in the fix commit stack trace).
- AC:LAttack complexity, low
- Once a forwarding host has XDP/TC metadata plus LWT encap routes, an attacker can repeatedly send matching traffic and deterministically hit the metadata/encap collision each time without races or victim-timed actions.
- PR:NPrivileges required, none
- The attacker only needs to send IP packets to a forwarding system; LWT routes, XDP/TC metadata programs, and forwarding are administrator deployment choices, not privileges the attacker must hold on the victim.
- UI:NUser interaction, none
- No end-user interaction is required beyond delivering attacker-controlled network packets to an affected router or edge node.
- S:UScope, unchanged
- Impact is confined to kernel network packet processing on the same host and does not cross VM, hypervisor, or sandbox security boundaries.
- C:HConfidentiality impact, high
- Non-BPF LWT encap silently overwrites metadata while meta_len can remain set, and BPF LWT xmit mishandles metadata via skb_data_move, enabling corrupted metadata reads by later BPF/TC code and potential information disclosure.
- I:HIntegrity impact, high
- LWT encapsulation performs headroom skb_push/bpf_skb_change_head over the metadata region without clearing meta_len, corrupting skb memory state in ways that can misdirect subsequent kernel/BPF packet-buffer writes.
- A:HAvailability impact, high
- The BPF LWT path triggers skb_data_move WARN_ON_ONCE in softirq and non-BPF encap corrupts forwarding skbs, enabling warn-driven failure modes and repeated disruption of packet forwarding on internet-facing edge routers.