GHSA-5jrj-52x8-m64h
GitHub Security Advisory
vyper performs multiple eval of `sqrt()` argument built in
Advisory Details
### Summary
Using the `sqrt` builtin can result in multiple eval evaluation of side effects when the argument has side-effects. The bug is more difficult (but not impossible!) to trigger as of 0.3.4, when the unique symbol fence was introduced (https://github.com/vyperlang/vyper/pull/2914).
A contract search was performed and no vulnerable contracts were found in production.
### Details
It can be seen that the `build_IR` function of the `sqrt` builtin doesn't cache the argument to the stack:
https://github.com/vyperlang/vyper/blob/4595938734d9988f8e46e8df38049ae0559abedb/vyper/builtins/functions.py#L2151
As such, it can be evaluated multiple times (instead of retrieving the value from the stack).
### PoC
With at least Vyper version `0.2.15+commit.6e7dba7` the following contract:
```vyper
c: uint256
@internal
def some_decimal() -> decimal:
self.c += 1
return 1.0
@external
def foo() -> uint256:
k: decimal = sqrt(self.some_decimal())
return self.c
```
passes the following test:
```solidity
// SPDX-License-Identifier: MIT
pragma solidity >=0.8.13;
import "../../lib/ds-test/test.sol";
import "../../lib/utils/Console.sol";
import "../../lib/utils/VyperDeployer.sol";
import "../ITest.sol";
contract ConTest is DSTest {
VyperDeployer vyperDeployer = new VyperDeployer();
ITest t;
function setUp() public {
t = ITest(vyperDeployer.deployContract("Test"));
}
function testFoo() public {
uint256 val = t.foo();
console.log(val);
assert (val == 4);
}
}
```
### Patches
Patched in https://github.com/vyperlang/vyper/pull/3976.
### Impact
No vulnerable production contracts were found.
Affected Packages
Related CVEs
Key Information
Dataset
Data from GitHub Advisory Database. This information is provided for research and educational purposes.