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INCIDENT REPLAY · 2026-08-28 (to about 2026-08-30)

Softaculous / Virtualizor hijack of a Hetzner /24

From 20:57 UTC a /24 more-specific of Hetzner space hosting Softaculous update, client and billing sites was announced with path ... 6204 62390 24940, forging Hetzner as origin. Hetzner's ROA for the /16 allowed lengths to /24, so the route validated. The attacker obtained a valid TLS certificate and delivered a malicious Virtualizor update to some installations.

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: Attacker via NexonHost (AS62390), upstream AS6204; Hetzner (AS24940) 162.55.80.0/24 inside 162.55.0.0/16; Softaculous and Virtualizor customers hurt

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 20:57 UTC a /24 more-specific of Hetzner space hosting Softaculous update, client and billing sites was announced with path ... 6204 62390 24940, forging Hetzner as origin. Hetzner's ROA for the /16 allowed lengths to /24, so the route validated. The attacker obtained a valid TLS certificate and delivered a malicious Virtualizor update to some installations.
  • Who: Attacker via NexonHost (AS62390), upstream AS6204; Hetzner (AS24940) 162.55.80.0/24 inside 162.55.0.0/16; Softaculous and Virtualizor customers hurt

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): UPSTREAM-1 (AS 64500, the upstream that accepted the path) has a session to HOSTER-1 (AS 64510, a small hosting customer) with a prefix-list of the customer's own block, a prefix limit, no AS-path filter, and a second session with every safeguard, so that each finding is one row.
  • This incident rests on one or two write-ups. The upstream accepted a path in which a small hosting customer transits for a major hosting AS: modelled as a customer session with a prefix filter and limit but no AS-path filter. The victim's loose ROA maxLength is the other auditable piece and is not covered: the audit has no ROA input.
  • 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.

UPSTREAM-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)
  • UPSTREAM-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: Auditable pieces: the upstream accepted a path in which a small hosting customer transits for a major hosting AS, and the victim's ROA maxLength was looser than what its routers announce.

Imported from docs/replays/hetzner-2026/FACTS.md and the replay manifests in the Hammerhead repository at commit 0ee9732.