Gravity Bridge was reported to have suffered a theft of roughly $5.4 million in what was described as a suspected signing-key compromise. The bridge was reportedly halted while validators investigated, which reflects how central signer trust is in cross-chain infrastructure.
This type of incident is not about a bug in the token itself; it is about control of the authorization path. If an attacker can obtain a signing key or equivalent privileged credential, they can approve transfers or state updates that look legitimate to the protocol.
The best defense is to reduce the power of any single key. Threshold signing, multisig approval, hardware security modules, strict key segregation, and continuous monitoring for abnormal signing behavior all make compromise harder to convert into a drain.
Bridge operators should also prepare for fast containment. Emergency pause mechanisms, signer revocation procedures, and pre-planned incident response can limit losses when a key is suspected to be compromised.