# CVE-2026-80612: net: lwtunnel: Drop skb metadata before LWT encapsulation

> A Linux kernel networking bug causes memory corruption and kernel warnings when forwarding packets with XDP metadata through LWT encapsulation.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Aug 2026
- **Updated:** 29 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-80612, GHSA-gcxj-phfp-fv28, UBUNTU-CVE-2026-80612

## What is CVE-2026-80612?

CVE-2026-80612 is a critical memory corruption vulnerability in Linux, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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).

## Which versions are affected by CVE-2026-80612?


## How do I fix CVE-2026-80612?

Apply the vendor's patch.

## Is CVE-2026-80612 being exploited?

There is no known exploitation of CVE-2026-80612 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80612 and fix it if it is affected.

What it is: CVE-2026-80612 is a critical memory corruption vulnerability in Linux, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-80612 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-80612/ (Markdown: https://insights.sbomify.com/CVE-2026-80612/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80612
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80612
- OSV: https://osv.dev/vulnerability/CVE-2026-80612

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80612/
Summaries are generated and may contain mistakes; the official description above is the record.