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vyper performs multiple eval of `sqrt()` argument built in

Moderate severity GitHub Reviewed Published Apr 25, 2024 in vyperlang/vyper • Updated Jun 18, 2024

Package

pip vyper (pip)

Affected versions

< 0.4.0

Patched versions

0.4.0

Description

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 (vyperlang/vyper#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);
    }
}

Patches

Patched in vyperlang/vyper#3976.

Impact

No vulnerable production contracts were found.

References

@charles-cooper charles-cooper published to vyperlang/vyper Apr 25, 2024
Published by the National Vulnerability Database Apr 25, 2024
Published to the GitHub Advisory Database Apr 25, 2024
Reviewed Apr 25, 2024
Last updated Jun 18, 2024

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS score

0.043%
(11th percentile)

Weaknesses

CVE ID

CVE-2024-32649

GHSA ID

GHSA-5jrj-52x8-m64h

Source code

Credits

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