OpenZeppelin Contracts using MerkleProof multiproofs may allow proving arbitrary leaves for specific trees
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 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 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 software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | @openzeppelin/contracts | >= 4.7.0, < 4.9.2 | 4.9.2 |
| npm package | @openzeppelin/contracts-upgradeable | >= 4.7.0, < 4.9.2 | 4.9.2 |
References
- https://github.com/OpenZeppelin/openzeppelin-contracts/security/advisories/GHSA-wprv-93r4-jj2p
- https://nvd.nist.gov/vuln/detail/CVE-2023-34459
- https://github.com/OpenZeppelin/openzeppelin-contracts/commit/4d2383e17186be3e8ccf5a442e9686ecc7de1c55
- https://github.com/OpenZeppelin/openzeppelin-contracts
- https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v4.9.2
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N- Weakness (CWE)
CWE-354- Platform
- npm
- Package
@openzeppelin/contracts, @openzeppelin/contracts-upgradeable- Disclosed
- 19.06.2023
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-wprv-93r4-jj2p - CC BY 4.0
Vulnerability history: @openzeppelin/contracts
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 20
- First → latest
- 08.2021 07.2025
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 2
- High 5
- Medium 12
- Low 1
Disclosures per year
- 2021: 4
- 2022: 7
- 2023: 7
- 2024: 1
- 2025: 1
- 2026: 0
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OpenZeppelin Contracts using MerkleProof multiproofs may allow proving arbitrary leaves for specific trees this entry
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