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9.8
CVE-2024-24563: Vyper permits negative array indexes leading to unintended actions
CVE-2024-24563 · published 2 years ago
Summary
The Vyper smart‑contract language lets developers use signed numbers as array indexes even though arrays are meant to be indexed with only non‑negative numbers. This can let contracts read or write unexpected storage slots, bypass safety checks, or become stuck in a denial‑of‑service loop. Until a patched release is available, avoid using unchecked indexes and add explicit checks that indexes are non‑negative before accessing arrays.
What to do
- Update vyper team vyper to version 0.4.0.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| pip | vyper team | vyper |
< 0.4.0 Fix: upgrade to 0.4.0
|
| – | vyperlang | vyper |
<= 0.3.10 cpe:2.3:a:vyperlang:vyper:*:*:*:*:*:python:*:* |
Original advisory text
Vyper array negative index vulnerability
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.
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.
References
- https://github.com/pypa/advisory-database/tree/main/vulns/vyper/PYSEC-2024-150.y...
- https://github.com/vyperlang/vyper/blob/a1fd228cb9936c3e4bbca6f3ee3fb4426ef45490... URL
- https://github.com/vyperlang/vyper/blob/c150fc49ee9375a930d177044559b83cb95f7963... URL
- https://github.com/advisories/GHSA-52xq-j7v9-v4v2
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/24xxx/CVE-2024-24563... Vendor Advisory
- https://github.com/vyperlang/vyper/security/advisories/GHSA-52xq-j7v9-v4v2 Vendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2024-24563 Vendor Advisory
Internet-facing
14 days
Internal
At next upgrade
- Not known to be exploited
- Needs hands-on effort to exploit
- Gives an attacker full control
Type
CWE-129Improper Validation of Array Index
Timeline
Published7 Feb 2024
Updated3 Nov 2026
First seen6 Mar 2026
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