Introduction:

In this post, we will discuss a recently discovered vulnerability (CVE-2024-26149) that affects the Vyper programming language. Vyper is a pythonic smart contract language designed for the Ethereum Virtual Machine (EVM). The language aims to provide a higher level of security and simplicity compared to other smart contract languages like Solidity. However, this vulnerability poses a severe threat to the contracts compiled with version .3.10 and earlier versions of Vyper that make use of arrays within _abi_decode.

Vulnerability Details

If an excessively large value is specified as the starting index for an array in _abi_decode, it can cause the read position to overflow. This results in the decoding of values outside the intended array bounds, potentially leading to exploitations in contracts that make use of arrays within _abi_decode.

To understand the vulnerability better, let's look at a code snippet that demonstrates the issue

# Vulnerable code in Vyper
@external
def set_array(data: Bytes[2048]):
    decoded_array: address[4] = _abi_decode(data, (address[4],))

In this example, the set_array function takes a parameter called data, which is expected to be decoded into an array of four addresses using the _abi_decode function. However, if the _abi_decode function is called with an unbounded starting index, the read position may overflow, and the decoding of values may occur outside the intended array bounds.

How to Exploit

An attacker can exploit this vulnerability by sending a crafted transaction to the vulnerable contract, providing data with a large starting index value. This can lead to unexpected contract behavior, like overwriting other contract storage slots or controlling contract execution in undesirable ways.

Mitigation

Developers using Vyper version .3.10 or earlier are encouraged to update their compilers to the latest version to avoid exposure to this vulnerability. Additionally, developers should review their smart contracts for any instances of _abi_decode and ensure that array bounds are appropriately defined and checked.

1. CVE-2024-26149 Official Record
2. Vyper GitHub Repository
3. Vyper Documentation

Conclusion

Although Vyper is designed to provide a higher level of security and simplicity for smart contracts, this example serves as a reminder that no programming language is perfect. Developers should always be vigilant and proactive in ensuring that their code is secure and up-to-date with the latest security patches and best practices. CVE-2024-26149 is a serious vulnerability that developers need to address promptly to ensure the continued security and stability of their smart contracts on the Ethereum platform.

Timeline

Published on: 02/26/2024 20:19:05 UTC
Last modified on: 02/26/2024 22:10:40 UTC