What happened
On April 13, 2026, an attacker forged a cross-chain message to Hyperbridge's Token Gateway on Ethereum, took admin control of the bridged DOT token, and minted 1 billion DOT. The bug was a missing bounds check in the Merkle Mountain Range (MMR) proof verifier used by HandlerV1: nothing required leaf_index < leafCount. A proof with leafCount = 1 and leaf_index = 1 made the root calculation skip the real leaf and accept a value the attacker supplied, so a fabricated request passed verification. The forged ChangeAssetAdmin request then went from the handler through the host to the gateway, which handed the attacker admin rights over the token.
The attacker sold the minted DOT into thin DEX liquidity for about 108 ETH. Hyperbridge first put the loss at about $237,000. About 245 ETH was also taken from the Token Gateway in a separate extraction: The Block reports it about an hour before the DOT mint, and Rekt attributes it to a different actor. Other gateway tokens (ARGN, MANTA, CERE) were minted as well. On April 16, Hyperbridge raised the loss estimate to about $2.5 million to include incentive pools on Ethereum, Base, BNB Chain and Arbitrum. Hyperbridge paused bridging. Native DOT on Polkadot was not affected.
Hyperbridge said a significant share of the funds had been traced to Binance, and it gave users who traded against the distorted DOT prices 14 days to return the funds voluntarily. It pledged to cover any remaining shortfall with its BRIDGE token one year after the exploit if recovery falls short.
**On-chain references**
- DOT mint and swap transaction:
0x240aeb9a8b2aabf64ed8e1e480d3e7be140cf530dc1e5606cb16671029401109 - Bridged DOT exploiter:
0xC513E4f5D7a93A1Dd5B7C4D9f6cC2F52d2F1F8E7 - Bridged DOT token:
0x8d010bf9c26881788b4e6bf5fd1bdc358c8f90b8
How it happened
- The attacker built an MMR proof with
leafCount = 1andleaf_index = 1. The verifier did not check that the index was in range, so the root calculation skipped the real leaf and used the attacker's supplied value, and the proof checked out. - Using that proof, they submitted a forged
ChangeAssetAdminrequest.HandlerV1accepted it and passed it through the host to the Token Gateway, which made the attacker admin of the bridged DOT token. - In one transaction at 03:55 UTC, the attacker's contract minted 1 billion bridged DOT and swapped it through Uniswap V4 and the Odos router for about 108 ETH.
- The same flaw was used to mint other gateway tokens and to take about 245 ETH from the Token Gateway, and incentive pools on four chains were hit, bringing the revised loss to about $2.5 million.
Protocol details
Evidence
- report @exvulsec incident report x.com
- report Hyperbridge - Rekt rekt.news
- report @hyperbridge incident report x.com
- report @PeckShieldAlert incident report x.com
- report @CertiKAlert incident report x.com
- transaction Etherscan transaction 0x240aeb9a...01109 (Bridged DOT Exploiter) etherscan.io
- analysis DeFiLlama defillama.com
- analysis Polkadot-based Hyperbridge revises exploit losses to $2.5 million, ten times initial estimate theblock.co
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