{"id":"CVE-2023-34459","aliases":["GHSA-wprv-93r4-jj2p"],"url":"https://o3.security/vulnerability/CVE-2023-34459","summary":"OpenZeppelin Contracts's MerkleProof multiproofs may allow proving arbitrary leaves for specific trees","details":"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.","published":"2023-06-16T22:13:18.181Z","modified":"2026-08-12T03:51:39.958587225Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"@openzeppelin/contracts","fixedVersion":"4.9.2"},{"ecosystem":"npm","name":"@openzeppelin/contracts-upgradeable","fixedVersion":"4.9.2"}],"fix":{"url":"https://github.com/OpenZeppelin/openzeppelin-contracts/commit/4d2383e17186be3e8ccf5a442e9686ecc7de1c55","label":"OpenZeppelin/openzeppelin-contracts@4d2383e"},"references":[{"type":"WEB","url":"https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v4.9.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/34xxx/CVE-2023-34459.json"},{"type":"ADVISORY","url":"https://github.com/OpenZeppelin/openzeppelin-contracts/security/advisories/GHSA-wprv-93r4-jj2p"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2023-34459"},{"type":"FIX","url":"https://github.com/OpenZeppelin/openzeppelin-contracts/commit/4d2383e17186be3e8ccf5a442e9686ecc7de1c55"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:39.958587225Z"}}