OAK — OnChain Attack Knowledge

Worked example · 2026-09

SingularityNET bridge — one stolen authorizer key, a signature that did not name the recipient, and no cap on the inbound path — SingularityNET Ethereum–Cardano bridge / Fetch.ai, NuNet, SingularityNET, World Mobile / Ethereum — 2026-09-19

Loss
8,721,530 FET (~$1.53–1.55M) drained from TokenConversionManagerV3 (0xab424A430CC09864fA1277A38193111705ADF3A3) in a single conversionIn call — the contract's entire FET balance. Within the same window the attacker minted 408.53M NTX (NuNet; ~42% of supply; ~$463K at mint, ~$1.44M realised in dumps), 260M AGIX and ~53.8M WMTx on Ethereum. Attacker-controlled holdings were reported at ~$16.77M, most of it newly minted tokens whose realisable value is far lower.
OAK Techniques observed
OAK-T10.001 (Validator / Signer Key Compromise — primary, operator-stated. Fetch.ai states the attack used "a stolen SingularityNET bridge authorizer key used to produce a valid signature for the converter call, alongside a separately compromised NuNet mint key used within the same window." The authorizer was reported as an offline, nonce-zero key existing solely to sign backend approvals. See techniques/T10.001-validator-signer-key-compromise.md). OAK-T5.003 (Hidden-Mint Dilution — effect-side, for the unbacked NTX / AGIX / WMTx mints dumped into liquidity).
Two design amplifiers, reported by on-chain analysts and not disputed by the teams
the authorizer's signature did not bind the recipient address, so a valid signature could pay any wallet; and conversionIn had no per-conversion limit, unlike conversionOut. The anomalous conversion ID also differed in format from the ~100 legitimate UUID-style IDs before it — a signal that was on-chain before the drain completed.
Attribution
pseudonymous. One wallet links the FET drain and the NTX mint.
Key teaching point
A single-signer bridge whose signature authorises "a conversion" rather than "this amount to this address" is a blank cheque, and the only question is who holds the pen. Key custody failed here, but key custody failing is the case bridge design exists for. What converted one stolen key into a full drain was that the signed message was under-specified and the inbound path was uncapped. Bind recipient and amount into the signed payload; rate-limit the inbound direction at least as tightly as the outbound; and rotate on suspicion — as of 2026-09-21, on-chain monitoring reported neither the authorizer nor the NuNet minter role had been rotated or revoked.

Summary

On the evening of 2026-09-19 a single call to conversionIn on the Ethereum side of the SingularityNET Ethereum–Cardano bridge paid out the contract's entire 8,721,530 FET to an attacker wallet, authorised by a valid signature from the bridge's conversion authorizer. About 29 minutes later the same wallet minted 408.53M NTX using a compromised NuNet minter key. Further unbacked mints of 260M AGIX and ~53.8M WMTx followed. Teams paused conversions and deactivated affected contracts.

Timeline (UTC, 2026-09-19 unless noted)

When Event OAK ref
undisclosed Bridge authorizer key and NuNet minter key compromised T10.001 (vector undisclosed)
evening conversionIn with valid signature and anomalous conversion ID drains 8,721,530 FET T10.001 — exploitation
+29 min 408.53M NTX minted to same wallet T5.003
09-19 → 09-20 260M AGIX and ~53.8M WMTx minted on Ethereum T5.003
09-20 → 21 Conversions paused; contracts deactivated; keys reported not yet rotated (response)

What defenders observed

  • The ID format was the tripwire. A conversion ID that did not match the format of every prior legitimate conversion is a cheap, exact anomaly. It fires on the first malicious call.
  • Two keys, one wallet, one half-hour. Separately held keys for separate projects compromised in the same window points to a shared custody environment upstream — the kind of co-location T11.011 describes — though no team has said so.
  • Minted value is not realised value. The $16.77M headline counts tokens at a price their dumping destroys; the realised figure is the FET drain plus what the mints sold for.

Public references

Techniques demonstrated (2)