On April 13, 2026, blockchain security firm Certik alerted the crypto community to a critical exploit in the Hyperbridge gateway that allowed an attacker to mint 1 billion unauthorized Polkadot (DOT) tokens on the Ethereum network. The news sent the price of DOT tumbling from $1.23 to $1.16, a decline of nearly 6%, before it recovered to $1.19 at press time.
Root Cause: Replay Vulnerability in Merkle Mountain Range Function
According to Certik's initial post-mortem, the exploit originated from a replay vulnerability in the calculateroot function of the Merkle Mountain Range library. This flaw meant that proofs were not properly bound to requests, allowing the attacker to reuse old state commitments from previous transactions. Downstream, the tokengateway.handlechangeadmin function failed to enforce strict input checks, enabling the attacker to arbitrarily inject request data. As a result, malicious code propagated unchecked through the system, ultimately granting the attacker administrative control over the bridged DOT contract on Ethereum. A single transaction then generated the 1 billion fake tokens.
Shallow Liquidity Capped Financial Damage
Despite the enormous number of tokens created, the attacker could not cash out at market value because the bridged version of DOT on Ethereum had extremely shallow liquidity. On-chain analytics firm Lookonchain confirmed that the hacker liquidated the entire 1 billion tokens in a single swap, yielding only approximately 108.2 Ether (about $237,000 at the time). Had the bridged asset been more widely traded, the financial impact could have been substantially higher. Industry observers noted that the shallow liquidity ironically acted as a circuit breaker, preventing catastrophic losses.
Core Relay Chain Unaffected; Patches Expected
Security experts were quick to clarify that the breach was localized to the Hyperbridge gateway on Ethereum. Polkadot’s core relay chain and the authentic DOT tokens residing on the Polkadot network remain secure and were not impacted. Certik noted: “The attacker submitted ‘proof’ value is copied from the ‘_stateCommitments’ in a previous tx… thus making the replay possible.” Hyperbridge has yet to release a full post-mortem, but developers are expected to implement patches to strengthen administrative smart contract functions and prevent similar exploits in the future.