{"cve":"CVE-2023-34459","nvd":{"published":"2023-06-16T23:15:08.817","modified":"2026-06-17T06:03:41.713","status":"Modified","description":"OpenZeppelin Contracts is a library for smart contract development. Starting in version 4.7.0 and prior to version 4.9.2, when the `verifyMultiProof`, `verifyMultiProofCalldata`, `procesprocessMultiProof`, or `processMultiProofCalldat` functions are in use, it is possible to construct merkle trees that allow forging a valid multiproof for an arbitrary set of leaves.\n\nA 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 inadvertedly 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.\n\nA 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.\n\nThe problem has been patched in version 4.9.2.\n\nSome workarounds are available. For those 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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N","score":5.9},"cwes":["CWE-354"],"references":["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/OpenZeppelin/openzeppelin-contracts/commit/4d2383e17186be3e8ccf5a442e9686ecc7de1c55","https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v4.9.2"],"products":["openzeppelin:contracts","openzeppelin:contracts_upgradeable"],"source":"nvd","synced_at":"2026-10-19T21:38:24.161619714+00:00"},"epss":{"cve":"CVE-2023-34459","score":0.00371,"percentile":0.31025,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-wprv-93r4-jj2p","url":"https://osv.dev/vulnerability/GHSA-wprv-93r4-jj2p","summary":"OpenZeppelin Contracts using MerkleProof multiproofs may allow proving arbitrary leaves for specific trees","modified":"2026-09-10T03:50:02.441943191Z","packages":[{"ecosystem":"npm","name":"@openzeppelin/contracts","purl":"pkg:npm/%40openzeppelin/contracts","ranges":[">=4.7.0 <4.9.2"],"fixed":["4.9.2"]},{"ecosystem":"npm","name":"@openzeppelin/contracts-upgradeable","purl":"pkg:npm/%40openzeppelin/contracts-upgradeable","ranges":[">=4.7.0 <4.9.2"],"fixed":["4.9.2"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}