Inline assembly uses return()/revert() to exit a function directly. This skips Solidity's normal epilogue (return-value packing, modifier post-code), so post-conditions and cleanup after the call site never execute.
// function f() external nonReentrant { assembly { return(0,0) } } // the nonReentrant modifier's lock-release epilogue is skipped -> the // guard can stay locked, bricking future calls.
// prefer Solidity return/revert; only use asm return/revert with full // awareness that trailing modifier/cleanup code is skipped.
Largest recorded losses in the same failure class — related, not the same bug:
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