Vyper's raw_call `value=` kwargs not disabled for static and delegate calls

Overview

Summary

Vyper compiler allows passing a value in builtin raw_call even if the call is a delegatecall or a staticcall. But in the context of delegatecall and staticcall the handling of value is not possible due to the semantics of the respective opcodes, and vyper will silently ignore the value= argument.

A contract search was performed and no vulnerable contracts were found in production.

Details

The IR for raw_call is built in the RawCall class: https://github.com/vyperlang/vyper/blob/9136169468f317a53b4e7448389aa315f90b95ba/vyper/builtins/functions.py#L1100

However, the compiler doesn't validate that if either delegatecall or staticall are provided as kwargs, that value wasn't set. For example, the following compiles without errors:

raw_call(self, call_data2, max_outsize=255, is_delegate_call=True, value=msg.value/2)

Impact

If the semantics of the EVM are unknown to the developer, he could suspect that by specifying the value kwarg, exactly the given amount will be sent along to the target. However in fact, no value will be sent.

Here is an example of an potentially problematic implementation of multicall utilizing the raw_call built-in:

value_accumulator: uint256 = empty(uint256)
    results: DynArray[Result, max_value(uint8)] = []
    return_data: Bytes[max_value(uint8)] = b""
    success: bool = empty(bool)
    for batch in data:
        msg_value: uint256 = batch.value
        value_accumulator = unsafe_add(value_accumulator, msg_value)
        if (batch.allow_failure == False):
            return_data = raw_call(self, batch.call_data, max_outsize=255, value=msg_value, is_delegate_call=True)
            success = True
            results.append(Result({success: success, return_data: return_data}))
        else:
            success, return_data = \
                raw_call(self, batch.call_data, max_outsize=255, value=msg_value, is_delegate_call=True, revert_on_failure=False)
            results.append(Result({success: success, return_data: return_data}))
    assert msg.value == value_accumulator, "Multicall: value mismatch"
    return results

Patches

Fixed in https://github.com/vyperlang/vyper/pull/3755

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading?

References

Are there any links users can visit to find out more?

Affected packages

• vyper < 0.4.0

Remediation

Upgrade to a patched release:

• vyper 0.4.0