CVE-2024-24563 Vyper array negative index vulnerability

What is CVE-2024-24563?

CVE-2024-24563 is a critical vulnerability in vyperlang vyper, published on 7 Feb 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine. Arrays can be keyed by a signed integer, while they are defined for unsigned integers only. The typechecker doesn't throw when spotting the usage of an `int` as an index for an array. The typechecker allows the usage of signed integers to be used as indexes to arrays. The vulnerability is present in different forms in all versions, including `0.3.10`. For ints, the 2's complement representation is used. Because the array was declared very large, the bounds checking will pass Negative values will simply be represented as very large numbers. As of time of publication, a fixed version does not exist.

There are three potential vulnerability classes: unpredictable behavior, accessing inaccessible elements and denial of service. Class 1: If it is possible to index an array with a negative integer without reverting, this is most likely not anticipated by the developer and such accesses can cause unpredictable behavior for the contract. Class 2: If a contract has an invariant in the form `assert index < x`, the developer will suppose that no elements on indexes `y | y >= x` are accessible. However, by using negative indexes, this can be bypassed. Class 3: If the index is dependent on the state of the contract, this poses a risk of denial of service. If the state of the contract can be manipulated in such way that the index will be forced to be negative, the array access can always revert (because most likely the array won't be declared extremely large). However, all these the scenarios are highly unlikely. Most likely behavior is a revert on the bounds check.

Weakness: CWE-129

Which versions are affected by CVE-2024-24563?

3 open source packages ship an affected version, including vyper. It affects 1 product.

Products include Vyperlang Vyper.

How do I fix CVE-2024-24563?

Upgrade vyper to a fixed version for your release line: 0.4.0 or 0.4.0b1.

Is CVE-2024-24563 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2024-24563 exists.

Other vulnerabilities in vyperlang vyper

• CVE-2024-24561 Vyper bounds check on built-in `slice()` function can be overflowed Critical 9.8
• CVE-2023-39363 Vyper incorrectly allocated named re-entrancy locks Critical 9.1
• CVE-2022-24845 Integer bounds error in Vyper High 8.8
• CVE-2022-29255 Multiple evaluation of contract address in call in vyper High 8.2
• CVE-2023-42443 Vyper vulnerable to memory corruption in certain builtins utilizing `msize` High 8.1

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-52xq-j7v9-v4v2, PYSEC-2024-150.