{"id":"CVE-2023-34459","aliases":["EUVD-2023-1907","GHSA-wprv-93r4-jj2p"],"status":"published","title":"OpenZeppelin Contracts's MerkleProof multiproofs may allow proving arbitrary leaves for specific trees","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.","severity":{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00371,"percentile":0.31403,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-354"],"published":"2023-06-16T22:13:18Z","modified":"2026-11-11T10:30:47Z","fixes":[{"ecosystem":"npm","package":"@openzeppelin/contracts","fixed_in":["4.9.2"],"sources":["ghsa","osv"]},{"ecosystem":"npm","package":"@openzeppelin/contracts-upgradeable","fixed_in":["4.9.2"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"npm","package":"@openzeppelin/contracts","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.7.0"},{"fixed":"4.9.2"}]}]},{"source":"ghsa","ecosystem":"npm","package":"@openzeppelin/contracts-upgradeable","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.7.0"},{"fixed":"4.9.2"}]}]},{"source":"osv","ecosystem":"npm","package":"@openzeppelin/contracts","ranges":[{"type":"SEMVER","events":[{"introduced":"4.7.0"},{"fixed":"4.9.2"}]}]},{"source":"osv","ecosystem":"npm","package":"@openzeppelin/contracts-upgradeable","ranges":[{"type":"SEMVER","events":[{"introduced":"4.7.0"},{"fixed":"4.9.2"}]}]}],"products":[{"vendor":"openzeppelin","product":"contracts"},{"vendor":"openzeppelin","product":"contracts_upgradeable"},{"vendor":"openzeppelin","product":"openzeppelin-contracts"}],"references":[{"url":"https://github.com/OpenZeppelin/openzeppelin-contracts/security/advisories/GHSA-wprv-93r4-jj2p","tags":["x_refsource_CONFIRM","x_transferred","Vendor Advisory","advisory","web"]},{"url":"https://github.com/OpenZeppelin/openzeppelin-contracts/commit/4d2383e17186be3e8ccf5a442e9686ecc7de1c55","tags":["x_refsource_MISC","x_transferred","Patch","fix","web"]},{"url":"https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v4.9.2","tags":["x_refsource_MISC","x_transferred","Release Notes","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2023-34459","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-wprv-93r4-jj2p"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2023/34xxx/CVE-2023-34459.json","tags":["advisory"]},{"url":"https://github.com/OpenZeppelin/openzeppelin-contracts","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2023-34459","title":"OpenZeppelin Contracts's MerkleProof multiproofs may allow proving arbitrary leaves for specific trees","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.","status":"published","published":"2023-06-16T22:13:18.181Z","modified":"2024-12-16T18:35:27.231Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-354"],"updated_at":"2026-11-02T14:35:35.580545Z"}],"euvd":[{"id":"EUVD-2023-1907","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.","status":"published","published":"2023-06-16T22:13:18Z","modified":"2024-12-16T18:35:27Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"updated_at":"2026-11-03T00:04:35.014369Z"}],"ghsa":[{"id":"GHSA-wprv-93r4-jj2p","title":"OpenZeppelin Contracts using MerkleProof multiproofs may allow proving arbitrary leaves for specific trees","description":"### Impact\n\nWhen 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.\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 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.\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](https://github.com/OpenZeppelin/merkle-tree) library are safe.\n\n### Patches\n\nThe problem has been patched in 4.9.2.\n\n### Workarounds\n\nIf 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.","status":"published","published":"2023-06-19T19:46:37Z","modified":"2023-11-08T05:04:00Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"cwes":["CWE-354"],"updated_at":"2026-11-02T14:37:16.721714Z"}],"nvd":[{"id":"CVE-2023-34459","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.","status":"published","published":"2023-06-16T23:15:08.817Z","modified":"2026-06-17T06:03:41.713Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"secondary"},{"version":"3.1","score":5.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-354"],"updated_at":"2026-11-02T14:08:06.335469Z"}],"osv":[{"id":"CVE-2023-34459","title":"OpenZeppelin Contracts's MerkleProof multiproofs may allow proving arbitrary leaves for specific trees","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.","status":"published","published":"2023-06-16T22:13:18.181Z","modified":"2026-11-11T10:30:47.71127989Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"cwes":["CWE-354"],"updated_at":"2026-11-11T11:06:24.990359Z"},{"id":"GHSA-wprv-93r4-jj2p","title":"OpenZeppelin Contracts using MerkleProof multiproofs may allow proving arbitrary leaves for specific trees","description":"### Impact\n\nWhen 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.\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 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.\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](https://github.com/OpenZeppelin/merkle-tree) library are safe.\n\n### Patches\n\nThe problem has been patched in 4.9.2.\n\n### Workarounds\n\nIf 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.","status":"published","published":"2023-06-19T19:46:37Z","modified":"2026-09-10T03:50:02.441943191Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"cwes":["CWE-354"],"updated_at":"2026-11-02T15:46:58.767335Z"}]}}