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What is a bridge hack?
A bridge hack is the theft of funds from a cross-chain bridge, the system that moves tokens between blockchains by locking them on one chain and issuing a stand-in on another. Bridges pool large deposits in one place, so a single stolen key or contract bug can empty them.
What it means for you
If you hold a bridged or wrapped token, its value depends on the bridge still holding the original coins. If those are stolen, your stand-in token can lose its backing even though it never left your wallet. You can check which bridge issued a token, how many signers control it, whether its contracts were audited and whether upgrades pass through a timelock.
How it works
Many bridges lock or burn assets on the source chain and mint matching tokens on the destination. Some rely on a small set of outside validators or a multisig to confirm deposits; ethereum.org notes these add trust assumptions and custodial risk, and that one flaw in a bridge contract can expose the funds. A review of 34 bridge exploits found leaked private keys of validators or deployers behind almost half; others came from signature checks that could be bypassed or from accepting messages without verifying their origin. When locked funds are drained, the minted tokens become unbacked.
Sources: ethereum.org: Introduction to blockchain bridges, ethereum.org developer docs: Bridges, SoK: Cross-Chain Bridging Architectural Design Flaws and Mitigations (arXiv) · checked 4 October 2026
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