Known failure classes.
WHAT REENTRANCY IS
A contract calling out to another, which calls back before the first finished updating.
WHAT IT PERMITS
Repeated withdrawal before balances are reduced.
WHAT PREVENTS IT
Updating state before making external calls, and reentrancy guards.
WHY IT REMAINS COMMON
It is easy to introduce and not visible on casual reading.
WHAT ACCESS CONTROL FAILURES ARE
Functions callable by anyone that should not be.
WHAT THEY PERMIT
Anything the function does, including draining or destroying.
WHAT ARITHMETIC ERRORS CAUSE
Values wrapping around, producing enormous or negative results.
WHAT ADDRESSES THEM
Language-level checks, present in modern versions.
WHAT ORACLE MANIPULATION IS
Influencing the external price a contract relies on.
HOW IT IS DONE
Temporarily moving the price on a source the contract reads.
WHAT PREVENTS IT
Prices from several sources, averaged over time.
WHAT FRONT-RUNNING IS
Observing a pending transaction and acting before it.
WHY IT IS POSSIBLE
Pending transactions are publicly visible.
WHAT IT PERMITS
Extracting value from others' trades.
WHAT LOGIC ERRORS PRODUCE
Behaviour that is technically correct and commercially wrong.
WHY AUDITS MATTER MOST FOR THOSE
Tools find patterns; people find intent mismatches.
