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INCIDENT REPLAY · 2025-04-01

Voxility (AS3223) DDoS-mitigation leak through Lumen

From 07:35 UTC for about 20 minutes AS3223 leaked 31,258 routes learned from peers to its transit provider Lumen. Traffic was drawn to Bucharest, where it was misdirected or dropped for lack of capacity.

Route leakLeak readvertisementCatalog confidence: high

A reconstruction, not the operator's network. Hammerhead's authors rebuilt the change from the public record as a small network of their own. No configuration here is the operator's. What follows is what the tool reported on that reconstruction; it is not a claim that the tool would have prevented the outage.

What happened

Who: Voxility (AS3223) caused; Lumen (AS3356) accepted and propagated; CENIC (AS2152), GTT (AS3257) and destinations in South Korea, Vietnam, Myanmar most affected

The summary at the top is paraphrased from the sources below. Hammerhead's catalog rates its confidence in this account high.

Sources

What the public record says

  • From 07:35 UTC for about 20 minutes AS3223 leaked 31,258 routes learned from peers to its transit provider Lumen. Traffic was drawn to Bucharest, where it was misdirected or dropped for lack of capacity.
  • Who: Voxility (AS3223) caused; Lumen (AS3356) accepted and propagated; CENIC (AS2152), GTT (AS3257) and destinations in South Korea, Vietnam, Myanmar most affected

What the reconstruction assumed

Decided by Hammerhead's authors to build a network that runs. None of it describes the operator's network.

Everything below is ours.

  • The family template (tools/replays/gen_family_leak.py): VOXILITY-1 (AS 3223) learns the victim's routes over a direct peering with the victim, and LUMEN-1 (AS 3356) prefers what VOXILITY-1 sends it and filters nothing on that session. A transit carries the victim's routes to the same network the ordinary way, and a third party sits behind it.
  • The edit is assumed. Before the change VOXILITY-1's export toward LUMEN-1 is a prefix-list permitting its own block; after it, the list is no longer attached. No operator in this family has published what was changed.
  • Cisco IOS syntax, and stand-in address space except where a prefix is on the record.
  • The accepting network's other sessions are filtered and limited, so that the audit's finding is about this session and not the template.
  • Lumen filtered by an AS-SET that expands to over a million entries, which filters nothing; here the session simply has no filter.

What Hammerhead said

Each run below is pinned by Hammerhead's replay tests at commit 0ee9732: the verdict and the quoted text are checked against the tool's output, and a run that disagrees fails the test. Reason lines are copied verbatim; a pinned line can be part of a longer reason. Every preflight run uses --max-blast-radius 100, so a change is never counted as caught merely because it touched many devices of a small network.

every network in one snapshot

now: fail

On the reconstruction, hammerhead preflight on a before and an after snapshot returned fail, for the reasons below.

Reason text pinned (some reason contains each line)

  • VOXILITY-1 would announce to 172.16.3.1 (AS 3356) routes it learns from other networks
  • path change:
  • now through AS 3223

First run, before the fixes this batch prompted

first: fail
  • forwarding-semantics gate: 1 device(s) changed configuration that reroutes or rewrites traffic without changing any route or ACL — VOXILITY-1: BGP peerings and their policy attachments pass --allow-flow-changes to accept it
  • path change: 1 destination(s) still delivered would be reached through a network their traffic does not cross today — 198.18.0.0/24 on PEER-1 (198.18.0.1) from LUMEN-1, X-1 now through AS 3223. No flow is lost, which is what a route leak looks like from inside the model. Pass --allow-path-changes if moving this traffic is intended

Pinned in tests/gauntlet/replays-leak.yaml.

VOXILITY-1's own router

now: fail

On the reconstruction, hammerhead preflight on a before and an after snapshot with --allow-flow-changes returned fail, for the reasons below.

Reason text pinned (some reason contains each line)

  • VOXILITY-1 would announce to 172.16.3.1 (AS 3356) routes it learns from other networks

First run, before the fixes this batch prompted

first: pass

Pinned in tests/gauntlet/replays-leak.yaml.

LUMEN-1's own router, no change: the audit

now: fail (finding)

An audit of one snapshot, no change: hammerhead nqe-library --mode run, check nqe.bgp.ebgp_peer_unfiltered_and_unlimited. Pinned status: fail, a finding whose evidence contains the text below.

Evidence pinned (the evidence contains each line)

  • LUMEN-1
  • 3223

First run, before the fixes this batch prompted

first: pass (no finding)

Pinned in tests/gauntlet/replays-leak.yaml.

Limits

  • The configurations are a reconstruction. Where the record is silent, the assumptions above fill the gap; if one is wrong, the replay is wrong in that respect.
  • A verdict describes the reconstructed network's converged state. Timing, traffic load, and anything a device does that no configuration states, such as software reacting to a health check or a firmware bug, are outside it.
  • A pass is reported as a pass. A fail says a gate fired on the reconstruction, nothing more.
  • Why the catalog counts this outage as in scope: Leaker's export policy is checkable, and the provider-side finding is new and concrete: a customer prefix filter so large it filters nothing.

Imported from docs/replays/voxility-2025/FACTS.md and the replay manifests in the Hammerhead repository at commit 0ee9732.