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INCIDENT REPLAY · 2018-05-31

Cloudflare 1.1.1.1 mitigated by its own DDoS system (Gatebot)

A deployment replaced Gatebot's hard-coded list of Cloudflare address ranges with a Provision API lookup but did not carry over the manual exception for the resolver ranges. Gatebot classified 1.1.1.1 traffic as an attack and applied DNS mitigations to it, making the resolver globally unreachable for 17 minutes.

Required flowNetwork automation pushed bad configCatalog 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: Cloudflare

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 deployment replaced Gatebot's hard-coded list of Cloudflare address ranges with a Provision API lookup but did not carry over the manual exception for the resolver ranges. Gatebot classified 1.1.1.1 traffic as an attack and applied DNS mitigations to it, making the resolver globally unreachable for 17 minutes.
  • Who: Cloudflare

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_policy.py): CLIENTS-1 (the clients) reaches RESOLVER-1 (the 1.1.1.1 resolver) through EDGE-1 (the edge the mitigation rule was pushed to), which filters inbound on its outside interface. The intent file names the flow: clients reach the resolver on udp/53.
  • The filter was generated at runtime by DDoS automation after a code deploy. What it generated is modelled as an ACL denying DNS to the resolver's prefix, gated as any other candidate would be; the intended mitigation denies one attacking range.
  • 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.

the change as intended

now: pass

On the reconstruction, hammerhead preflight on a before and an after snapshot with --policy @cloudflare_gatebot_2018/policy.yaml --allow-flow-changes returned pass.

First run, before the fixes this batch prompted

first: pass

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

the change as pushed

now: fail

On the reconstruction, hammerhead preflight on a before and an after snapshot with --policy @cloudflare_gatebot_2018/policy.yaml --allow-flow-changes returned fail, for the reasons below.

Reason text pinned (some reason contains each line)

  • policy gate: high/critical failure(s) on the 'after' network: clients reach the resolver
  • NOT reachable (expected reachable)

First run, before the fixes this batch prompted

first: fail
  • reachability regression: 1 connected subnet(s) reachable before are not reachable after — 198.18.0.0/24 on RESOLVER-1 (198.18.0.1) from CLIENTS-1 [udp/53 dns]

Pinned in tests/gauntlet/replays-policy.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.

A flow rule names its protocol and port

Every reachability rule probed TCP/80, so an intent about SIP could not tell the push from the intended change: 7 of 11 intended changes failed on main and the one that dropped only the named port passed. protocol: and dst_port: on the rule; the policy gate's reason now carries the violation, not only the policy's name.

Found by: Required-flow 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 effect is a filter blocking needed traffic, but it was generated at runtime by DDoS automation after a code deploy; there was no static candidate config to verify beforehand.

Imported from docs/replays/cloudflare-gatebot-2018/FACTS.md and the replay manifests in the Hammerhead repository at commit 0ee9732.