CVE-2023-34459
OpenZeppelin Contracts using MerkleProof multiproofs may allow proving arbitrary leaves for specific trees
Impact
### Impact When the `verifyMultiProof`, `verifyMultiProofCalldata`, `processMultiProof`, or `processMultiProofCalldata` functions are in use, it is possible to construct merkle trees that allow forging a valid multiproof for an arbitrary set of leaves. A contract may be vulnerable if it uses multiproofs for verification and the merkle tree that is processed includes a node with value 0 at depth 1 (just under the root). This could happen inadvertently for balanced trees with 3 leaves or less, if the leaves are not hashed. This could happen deliberately if a malicious tree builder includes such a node in the tree. A contract is not vulnerable if it uses single-leaf proving (`verify`, `verifyCalldata`, `processProof`, or `processProofCalldata`), or if it uses multiproofs with a known tree that has hashed leaves. Standard merkle trees produced or validated with the [@openzeppelin/merkle-tree](https://github.com/OpenZeppelin/merkle-tree) library are safe. ### Patches The problem has been patched in 4.9.2. ### Workarounds If you are using multiproofs: When constructing merkle trees hash the leaves and do not insert empty nodes in your trees. Using the [@openzeppelin/merkle-tree](https://www.npmjs.com/package/@openzeppelin/merkle-tree) package eliminates this issue. Do not accept user-provided merkle roots without reconstructing at least the first level of the tree. Verify the merkle tree structure by reconstructing it from the leaves.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| npm | @openzeppelin/contracts | >= 4.7.0, < 4.9.2 | 4.9.2 |
| npm | @openzeppelin/contracts-upgradeable | >= 4.7.0, < 4.9.2 | 4.9.2 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Openzeppelin | Contracts | from 4.7.0 before 4.9.2 |
| Openzeppelin | Contracts Upgradeable | from 4.7.0 before 4.9.2 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/OpenZeppelin/openzeppelin-contracts/commit/4d2383e17186be3e8ccf5a442e9686ecc7de1c55
- https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v4.9.2
- https://github.com/OpenZeppelin/openzeppelin-contracts/security/advisories/GHSA-wprv-93r4-jj2p
- https://github.com/advisories/GHSA-wprv-93r4-jj2p
- https://nvd.nist.gov/vuln/detail/CVE-2023-34459