CVE-2024-32647: vyper performs double eval of raw_args in create_from_blueprint

First published: Thu Apr 25 2024(Updated: )

### Summary Using the `create_from_blueprint` builtin can result in a double eval vulnerability when `raw_args=True` and the `args` argument has side-effects. A contract search was performed and no vulnerable contracts were found in production. In particular, the `raw_args` variant of `create_from_blueprint` was not found to be used in production. ### Details It can be seen that the `_build_create_IR` function of the `create_from_blueprint` builtin doesn't cache the mentioned `args` argument to the stack: https://github.com/vyperlang/vyper/blob/cedf7087e68e67c7bfbd47ae95dcb16b81ad2e02/vyper/builtins/functions.py#L1847 As such, it can be evaluated multiple times (instead of retrieving the value from the stack). ### PoC The vulnerability is demonstrated in the following `boa` test: ``` vyper src1 = """ c: uint256 """ deployer = """ created_address: public(address) deployed: public(uint256) @external def get() -> Bytes[32]: self.deployed += 1 return b'' @external def create_(target: address): self.created_address = create_from_blueprint(target, raw_call(self, method_id("get()"), max_outsize=32), raw_args=True, code_offset=3) """ Factory = b.loads_partial(src1) c = Factory.deploy_as_blueprint() c2 = b.loads(deployer, b'') c2.create_(c) c2.deployed() ``` The output of `c2.deployed()` is `2` although `create_` was called only once and the value was initialized to `0`. ### Patches Patched in https://github.com/vyperlang/vyper/pull/3976. ### Impact No vulnerable production contracts were found. Additionally, double evaluation of side-effects should be easily discoverable in client tests. As such, the impact is `low`.

Credit: security-advisories@github.com security-advisories@github.com

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