MakerDAO flip keeper: an unprotected function handed an attacker control of dormant auction winnings

Funds gone. The adapter contract the attacker created still holds delegation over the keeper's Vat account (confirmed on-chain on 19 October 2026). We found no statement from MakerDAO or Sky, or from the keeper's operator.

1. 2020-03-12 15:36 UTCThe keeper places the winning bid on ETH-A auction 1457 (50 WETH lot).
2. 2020-03-15 15:26 UTCBidding on auction 1457 ends. The keeper never settles it, and three more auctions (1458 to 1460) go the same way, per the analyses.
3. 2026-10-06Public alerts appear; CertiK publishes its analysis.
4. 2026-10-06 05:57 UTCThe attacker's wallet is funded; its balance goes from zero to about 0.098 ETH in this block.
5. 2026-10-06 06:12 UTCThe attacker deploys the helper contract.
6. 2026-10-06 06:13 UTCExploit transaction: 200 ETH reaches the attacker's wallet.
7. 2026-10-06 06:19 UTCFirst of the 10 ETH deposits to a mixer router.

The keeper implementation exposes a function that calls the Vat's hope() on a caller-supplied address and then calls back into that address, without the ds-auth check its other privileged functions carry. Two independent analyses agree. We confirmed the selector is in the implementation and that an unrelated, freshly funded account executed it successfully; we did not decompile the bytecode ourselves.

Basis: independent analysis · verified by us against that source

Classes: Access control and caller trust

• The keeper still held unsettled claims: four auctions it had won in 2020 where the collateral sat in the retired Flipper, uncollected.
• The keeper's implementation exposed a function that grants Vat rights to any address passed in, and then calls back into that address.
• Auction settlement and collateral exit in the Vat and GemJoin are permissionless once rights are granted, so nothing else had to be bypassed.
• No funding, flash loan or special position was needed. The attacker's wallet held about 0.1 ETH for fees.

1. The attacker deployed a helper contract, then in one transaction had it create an adapter contract that knew the Flipper, Vat, GemJoin, WETH and the four auction ids.
2. The helper called the keeper's unprotected function with the adapter's address. The keeper granted the adapter rights over its own Vat account and then called back into it.
3. With those rights active, the adapter settled the four old auctions, which credited 200 WETH of collateral to the keeper inside the Vat, moved it to itself, and exited it through GemJoin.
4. The WETH was unwrapped and 200 ETH was forwarded to the attacker's wallet in the same transaction. The rights were never revoked.

A description of the flow for defenders. It leaves out calldata and anything needed to reproduce it.

200 ETH of collateral credited to a dormant keeper by four auctions it won in March 2020 and never settled. No MakerDAO core funds were lost, per the analyses we read.

Method: Native amount from the transaction receipt and the attacker wallet's balance change at the exploit block (200.0 ETH net of gas). The dollar figure is CertiK's, priced at the time of the exploit; other alerts say about $538K. We do not convert prices ourselves.

Loss and recovery are separate figures. They are never netted, and amounts in different currencies are never added together.

• verified200 ETH moved from the auction path to the attacker's wallet in a single transaction (block 26131471, 2026-10-06 06:13:11 UTC).Receipt, block and balance change read from a public node.
• verifiedThe Flipper's record for auction 1457 listed the keeper as winner with a 50 WETH lot before the block and was cleared after it.Read-only eth_call at the blocks before and after. Only 1457 was read; the receipt shows four settlement events from the Flipper.
• verifiedThe keeper still grants the adapter rights in the Vat.Vat.can(keeper, adapter) returned 1 after the exploit block and still does on 19 October 2026.
• reportedFunction 0x8804d1de has no authorisation check.CertiK and the repository author's decompile. We found the selector in the implementation and saw an unrelated account call it successfully; we did not decompile it.
• reportedThe implementation source is unverified.CertiK. We did not check the explorer.
• estimateThe loss was about $543K.CertiK's $542,982 at the time; other alerts say about $538K. Dollar values depend on the price used.
• reportedThe proceeds went to a mixer in 10 ETH lots, twenty in total.CertiK and SentinelTX. We confirmed the first 10 ETH deposit only.
• unknownThe keeper's operator knew of the flaw or can recover anything.No statement found.
• hypothesisOther dormant keepers from the same period carry the same flaw.Plausible, since keeper code was often reused, but nothing we read tests it.

• Guarded delegation pattern (illustrative)Defensive pattern
• src/test/2026-10/MakerDAOFlipKeeper_exp.solPublic reproduction file — open in the code reader

• No fix, revocation or statement from the keeper's operator or from MakerDAO or Sky was found. The adapter's rights over the keeper's Vat account were still in place on 19 October 2026. (none found)
• Prevention for similar keepers: gate any function that grants Vat rights or calls back into a supplied address, revoke delegations after use, and settle or sweep won auctions. (recommendation)

• On-chain data

  ThreatWire: Read-only lookups of the exploit transaction, receipt, balances, Flipper record, proxy implementation slot and Vat delegation

  Published 2026-10-19 · retrieved 2026-10-19 · Public JSON-RPC nodes. No code executed.

• Independent analysis

  CertiK: MakerDAO Legacy Auction Keeper Incident Analysis

  Published 2026-10-06 · retrieved 2026-10-19 · Primary technical analysis: attack flow, addresses, root cause, fund flow.

• Independent analysis

  Olympix: MakerDAO keeper loss and how it could have been prevented

  Published 2026-10-06 · retrieved 2026-10-19 · Same mechanism; adds the timeline of the attacker wallet. Vendor post.

• Independent analysis

  SentinelTX via ChainBounty: Third-party MakerDAO keeper exploit sends 200 ETH to Tornado Cash

  retrieved 2026-10-19 · Call-trace reading of the proxy delegatecall; notes that function names are inferred from selectors.

• Media report

  The Crypto Times: Dormant MakerDAO keeper drained of $538K, core remains intact

  Published 2026-10-06 · retrieved 2026-10-19 · Quotes the first public alert; source of the $538K rounding.

• Media report

  SlowMist Hacked: MakerDAO ETH-A Liquidation Keeper Bot entry

  Published 2026-10-06 · retrieved 2026-10-19 · Incident database entry; loss listed as $538K.

• Repository entry

  DeFiHackLabs (pinned file): Reproduction file listed for this incident

  Published 2026-10-06 · retrieved 2026-10-19 · Repository claim, not proof. Linked to the exact commit for traceability. We did not run it.

• FlashLoopAdapter: a spoofable caller check in a Safe moduleShared class: Access control and caller trust