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:
- 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:
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
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).
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (9.8): severity, escalated by confirmed exploitation. This CVE's 9.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 9.8 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.6% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-01). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it