unchecked-return-values

An unchecked return value vulnerability in Solidity occurs when low-level calls like `.call()`, `.send()`, or `.delegatecall()` execute without verifying their boolean success status, potentially leading to unexpected state changes and contract exploits.

To audit Solidity code for unchecked low-level calls, scan the contract for `.call()`, `.send()`, and `.delegatecall()` invocations and flag instances where the boolean return value indicating success or failure is not explicitly checked.

Ignoring the return value of a low-level call causes state inconsistencies because the called function may fail silently without reverting the transaction, allowing subsequent contract logic to execute based on a false assumption of successful state modification.

Unchecked call detection maps directly to SWC-104 guidelines, assigning a 'Medium' severity and 'High' confidence rating to vulnerabilities where `.call()`, `.send()`, or `.delegatecall()` success statuses are ignored.

You need to check the return value of `.send()` when handling external interactions because it returns a boolean on failure instead of reverting, whereas `.transfer()` automatically reverts on failure and does not require explicit return value checks.

The limitation of detecting unchecked calls is that it primarily targets `.call()`, `.send()`, and `.delegatecall()` syntax patterns, meaning complex logic hiding failed state updates through alternative mechanisms may not be flagged under SWC-104 rules.