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INCIDENT REPLAY · 2013-03-21

CB3ROB hijacks a Spamhaus name-server /32

During the large DDoS against Spamhaus, AS34109 announced a /32 for one Spamhaus DNS server and answered every blocklist query with a positive result (127.0.0.2). Networks that accepted the /32 over peering got wrong spam verdicts.

Accepting networkMalicious deliberateCatalog confidence: medium

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: CB3ROB / CyberBunker (AS34109) caused; Spamhaus 204.16.254.40 (0.ns.spamhaus.org) targeted; peers at an exchange, including Greenhost, received the route

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

Sources

What the public record says

  • During the large DDoS against Spamhaus, AS34109 announced a /32 for one Spamhaus DNS server and answered every blocklist query with a positive result (127.0.0.2). Networks that accepted the /32 over peering got wrong spam verdicts.
  • Who: CB3ROB / CyberBunker (AS34109) caused; Spamhaus 204.16.254.40 (0.ns.spamhaus.org) targeted; peers at an exchange, including Greenhost, received the route

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_audit.py): IX-PEER-1 (AS 64500, a network that accepted the /32 over a peering session) has a session to CB3ROB-1 (AS 34109, CB3ROB, announcing one address) with a prefix-list that permits any prefix of any length, a prefix limit, an inbound AS-path filter, and a second session with every safeguard, so that each finding is one row.
  • A /32 was accepted. The accepting session's filter is modelled as permitting any length (le 32), which is the one-line finding the record points at.
  • No change is replayed: the announcing network's change is not ours to gate. The audit runs on the accepting router's healthy configuration.
  • Cisco IOS syntax and stand-in address space throughout. A reconstruction, not any operator's configuration.

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.

IX-PEER-1's own router, no change: the inbound filter accepts prefixes longer than /24

now: fail (finding)

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

Evidence pinned (the evidence contains each line)

  • 1 row(s)
  • IX-PEER-1
  • 34109

First run, before the fixes this batch prompted

first: skipped-stub (the check was a stub)

Need per-peer prefix-list length introspection.

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

What changed in Hammerhead because of it

From the “What was fixed” table in Hammerhead's replay notes, where each fix landed after a failing test. “Found by” is copied as written; a family name means the batch this incident belongs to.

Inbound max prefix length and AS-path filter on BgpSession

prefix_list_max_length and a new ebgp_inbound_as_path_filter audit stop being stubs: a /32 for somebody else's address wins by longest match wherever it is accepted; a prefix filter generated from a forged registry object says nothing about whose path.

Found by: Accepting-network family

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 partly in scope: The accepting networks had no maximum-length (le 24) filter on peering sessions, a one-line audit finding; the attacker's change itself is not reviewable.

Imported from docs/replays/cb3rob-2013/FACTS.md and the replay manifests in the Hammerhead repository at commit 0ee9732.