Ecosyste.ms: Advisories

Security Advisories: GSA_kwCzR0hTQS01anJqLTUyeDgtbTY0aM4AA7UF

vyper performs double eval of the argument of sqrt

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:

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:

// 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);
    }
}

Impact

No vulnerable production contracts were found.

Permalink: https://github.com/advisories/GHSA-5jrj-52x8-m64h
JSON: https://advisories.ecosyste.ms/api/v1/advisories/GSA_kwCzR0hTQS01anJqLTUyeDgtbTY0aM4AA7UF
Source: GitHub Advisory Database
Origin: Unspecified
Severity: Moderate
Classification: General
Published: 11 days ago
Updated: 11 days ago

CVSS Score: 5.3
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Identifiers: GHSA-5jrj-52x8-m64h, CVE-2024-32649
References:

• https://github.com/vyperlang/vyper/security/advisories/GHSA-5jrj-52x8-m64h
• https://nvd.nist.gov/vuln/detail/CVE-2024-32649
• https://github.com/vyperlang/vyper/pull/2914
• https://github.com/advisories/GHSA-5jrj-52x8-m64h

Repository: https://github.com/vyperlang/vyper
Blast Radius: 12.6

Affected Packages