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INCIDENT REPLAY · 2008-08-10

Pilosov-Kapela DEFCON man-in-the-middle demonstration

A live, authorised demonstration that an attacker can announce a more-specific of a victim prefix, use AS-path poisoning so one upstream keeps a clean return path, and forward intercepted traffic on to the victim, hiding the detour by adjusting TTL. The slides show the ALTDB route object being added with no verification.

Accepting networkMalicious deliberateCatalog 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: Alex Pilosov and Tony Kapela (demonstrators); DEFCON conference network prefix 24.120.56.0/24 registered to AS26627 in ALTDB as the consenting target

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

  • A live, authorised demonstration that an attacker can announce a more-specific of a victim prefix, use AS-path poisoning so one upstream keeps a clean return path, and forward intercepted traffic on to the victim, hiding the detour by adjusting TTL. The slides show the ALTDB route object being added with no verification.
  • Who: Alex Pilosov and Tony Kapela (demonstrators); DEFCON conference network prefix 24.120.56.0/24 registered to AS26627 in ALTDB as the consenting target

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): TRANSIT-1 (AS 64500, a transit provider with the customer sessions the talk describes) has a session to ATTACKER-1 (AS 64510, the demonstrating network) with no inbound prefix filter, a prefix limit, no AS-path filter, and a second session with every safeguard, so that each finding is one row.
  • The talk's enabling gaps: customer sessions with only a prefix limit, no prefix filter, and no filtering of the provider's own prefixes or of the AS path. Modelled as such.
  • 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.

TRANSIT-1's own router, no change: no inbound filter

now: fail (finding)

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

Evidence pinned (the evidence contains each line)

  • 1 row(s)
  • TRANSIT-1
  • 64510

First run, before the fixes this batch prompted

first: fail (finding)

1 row(s) returned (expected 0); first: s.device=TRANSIT-1 s.peer=172.16.0.2 s.remote_as=64510

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

TRANSIT-1's own router, no change: no AS-path filter on the way in

now: fail (finding)

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

Evidence pinned (the evidence contains each line)

  • 1 row(s)
  • TRANSIT-1
  • 64510

First run, before the fixes this batch prompted

first: no-such-check (the check did not exist yet)

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 attacker's side is out of reach, but the enabling gaps the slides list (customer sessions with only max-prefix, no filtering of one's own prefixes inbound from external peers) are exactly what a config audit reports.

Imported from docs/replays/pilosov-kapela-2008/FACTS.md and the replay manifests in the Hammerhead repository at commit 0ee9732.