CVE-2023-46247: Vyper has incorrect storage layout for contracts containing large arrays
First published: Wed Dec 13 2023(Updated: )
### Impact contracts containing large arrays might underallocate the number of slots they need. prior to v0.3.8, the calculation to determine how many slots a storage variable needed used `math.ceil(type_.size_in_bytes / 32)`: https://github.com/vyperlang/vyper/blob/6020b8bbf66b062d299d87bc7e4eddc4c9d1c157/vyper/semantics/validation/data_positions.py#L197 the intermediate floating point step can produce a rounding error if there are enough bits set in the IEEE-754 mantissa. roughly speaking, if `type_.size_in_bytes` is large (> 2**46), and slightly less than a power of 2, the calculation can overestimate how many slots are needed. if `type_.size_in_bytes` is slightly more than a power of 2, the calculation can underestimate how many slots are needed. the following two example contracts can result in overwriting of the variable `vulnerable`: ```vyper large_array: address[2**64 + 1] # type_.size_in_bytes == 32 * (2**64 + 1); math.ceil(type_.size_in_bytes / 32) < 2**64 + 1 vulnerable: uint256 # writing to self.large_array[2**64] will overwrite self.vulnerable ``` ```vyper large_dynarray: DynArray[address, 2**64] # Dynarray has a length word in front, its size in bytes is 32 * (2**64 + 1) vulnerable: uint256 # writing to self.large_dynarray[2**64 - 1] will overwrite self.vulnerable ``` note that in the latter case, the risk of `vulnerable` being overwritten is relatively small, since it would cost roughly $1.45 million trillion USD at today's gas prices (gas price 20gwei, ETH ~= $1800) in order to extend the DynArray to its full container size. ### Patches patched by v0.3.8, specifically in commit https://github.com/vyperlang/vyper/commit/0bb7203b584e771b23536ba065a6efda457161bb.
Credit: security-advisories@github.com security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| pip/vyper | <=0.3.7 | 0.3.8 |
| Vyper | <0.3.8 |
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Reference Links
- https://github.com/vyperlang/vyper/blob/6020b8bbf66b062d299d87bc7e4eddc4c9d1c157/vyper/semantics/validation/data_positions.py#L197
- https://github.com/vyperlang/vyper/commit/0bb7203b584e771b23536ba065a6efda457161bb
- https://github.com/vyperlang/vyper/security/advisories/GHSA-6m97-7527-mh74
- https://nvd.nist.gov/vuln/detail/CVE-2023-46247
- https://github.com/advisories/GHSA-6m97-7527-mh74 (Advisory)
- https://github.com/pypa/advisory-database/tree/main/vulns/vyper/PYSEC-2023-307.yaml
Frequently Asked Questions
What is the severity of CVE-2023-46247?
CVE-2023-46247 is classified as a vulnerability that causes underallocation of storage slots in smart contracts.
How do I fix CVE-2023-46247?
To fix CVE-2023-46247, upgrade to Vyper version 0.3.8 or later.
What can be exploited in CVE-2023-46247?
CVE-2023-46247 can be exploited by contracts that utilize large arrays, leading to potential storage issues.
Which versions of Vyper are affected by CVE-2023-46247?
CVE-2023-46247 affects Vyper versions prior to 0.3.8.
Is there a known workaround for CVE-2023-46247?
There is no documented workaround for CVE-2023-46247; upgrading to the fixed version is recommended.
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