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INCIDENT REPLAY · 2017-05-12

WannaCry in the NHS (Internet-facing firewall exposure)

At least 81 of 236 English trusts and 603 primary-care and other organisations (595 GP practices) were infected or disrupted; NHS England identified 6,912 cancelled appointments and estimated more than 19,000 in total. Five A&E departments diverted patients.

Required flowACL / firewall ruleCatalog 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: NHS England trusts and GP practices; NHS Digital

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

  • At least 81 of 236 English trusts and 603 primary-care and other organisations (595 GP practices) were infected or disrupted; NHS England identified 6,912 cancelled appointments and estimated more than 19,000 in total. Five A&E departments diverted patients.
  • Who: NHS England trusts and GP practices; NHS Digital

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): INTERNET-1 (the internet) reaches WARD-HOSTS-1 (hosts on the trust's network) through TRUST-FW-1 (the trust's internet firewall), which filters inbound on its outside interface. The intent file names the flow: SMB is not reachable from the internet on tcp/445.
  • Not a change. The standing exposure, SMB reachable from the internet, is written as an isolation rule and run against the healthy configuration. The firewall's inbound ACL permits TCP 445 from anywhere, which is the exposure the record describes.
  • 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.

no change: the isolation rule against the healthy configuration

now: fail

On the reconstruction, hammerhead preflight on a before and an after snapshot with --policy @wannacry_nhs_2017/policy.yaml returned fail, for the reasons below.

Reason text pinned (some reason contains each line)

  • policy gate: high/critical failure(s) on the 'after' network: SMB is not reachable from the internet
  • IS reachable (expected isolation)

First run, before the fixes this batch prompted

first: pass

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: Not an outage caused by a push, but SMB (TCP 445) reachable from the Internet or across trust zones is a standing firewall finding that a segmentation audit reports.

Imported from docs/replays/wannacry-nhs-2017/FACTS.md and the replay manifests in the Hammerhead repository at commit 0ee9732.