On April 13, blockchain security firm Certik disclosed a major exploit: a hacker had used a vulnerability in the Hyperbridge gateway to mint 1 billion unauthorized Polkadot (DOT) tokens on the Ethereum network. The news triggered a 6% price drop in DOT, from $1.23 to $1.16, though the token later recovered to $1.19 as of press time.
Exploit Details and Attack Vector
According to Certik's initial analysis, the vulnerability was a “replay attack” flaw in Hyperbridge's Merkle Mountain Range function. The attacker forged a message to gain admin privileges over the bridged DOT contract on Ethereum, then executed a single transaction to mint 1 billion fake tokens. Certik noted that the “proof” value sent by the attacker was copied from “_stateCommitments” in a previous transaction, allowing reuse of old state commitments and bypassing validation.
Furthermore, the tokengateway.handlechangeadmin function lacked rigorous input checks, enabling the attacker to arbitrarily inject request data. This ultimately allowed the malicious code to change the DOT token admin address.
Market Impact and Liquidity Bottleneck
Despite the massive minting (1 billion tokens), the attacker did not reap huge profits. On-chain analyst Lookonchain confirmed that the hacker sold all fake DOT in a single swap, obtaining approximately 108.2 ETH (~$237,000). The reason was the extremely low liquidity of the bridged DOT on Ethereum, which could not support a sell-off of such magnitude. Had the bridged asset enjoyed mainstream-level liquidity, the financial damage would have been substantially larger.
Security Experts: Polkadot Mainnet Safe
Multiple security experts quickly clarified that the exploit was confined to the Hyperbridge gateway on Ethereum. Polkadot's relay chain and native DOT tokens remain completely unaffected. Certik stated, “The main Polkadot chain and relay chain are secure.” Hyperbridge has not yet published a full post-mortem, but patches are expected to protect smart contract admin functions from similar attacks.
Lessons Learned
This incident once again highlights the fragility of cross-chain bridge smart contracts. Although Hyperbridge operates on multiple chains (Polygon, BNB Chain, etc.), this bug only impacted the Ethereum bridge. While DOT holders can rest assured that mainnet assets are safe, investors should remain cautious about liquidity risks associated with bridged tokens.