Cosmos EVM Module Bug Brings Four Blockchains Offline

A shared bug in the Cosmos EVM module has caused four blockchains to go offline simultaneously. The affected chains are KiiChain, TAC, MANTRA, and Nesa.

The issue was identified as a weakness in the balance handling around vesting accounts and staking operations, which allowed attackers to drain funds from user wallets. In the case of KiiChain, an attacker used this technique 18 times on August 22, draining over $148 million worth of KII tokens before validators halted the network.

TAC also reported a loss of approximately $7.5 million in TAC tokens due to a precompile-layer weakness. MANTRA and Nesa detected malicious activity tied to a Cosmos EVM vulnerability and paused block production before applying software fixes.

Cosmos Labs has been criticized for publishing a fix for the bug on August 19 without giving downstream chains private advance notice or marking the release as security critical, which could have given attackers an advantage. The company has promised to publish a full incident report once the situation is resolved.