{"id":"GHSA-wprv-93r4-jj2p","summary":"OpenZeppelin Contracts using MerkleProof multiproofs may allow proving arbitrary leaves for specific trees","details":"### 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.","aliases":["CVE-2023-34459"],"modified":"2026-09-10T03:50:02.441943191Z","published":"2023-06-19T19:46:37Z","database_specific":{"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2023-06-19T19:46:37Z","nvd_published_at":"2023-06-16T23:15:08Z","cwe_ids":["CWE-354"]},"references":[{"type":"WEB","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":"WEB","url":"https://github.com/OpenZeppelin/openzeppelin-contracts/commit/4d2383e17186be3e8ccf5a442e9686ecc7de1c55"},{"type":"PACKAGE","url":"https://github.com/OpenZeppelin/openzeppelin-contracts"},{"type":"WEB","url":"https://github.com/OpenZeppelin/openzeppelin-contracts/releases/tag/v4.9.2"}],"affected":[{"package":{"name":"@openzeppelin/contracts","ecosystem":"npm","purl":"pkg:npm/%40openzeppelin/contracts"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.7.0"},{"fixed":"4.9.2"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2023/06/GHSA-wprv-93r4-jj2p/GHSA-wprv-93r4-jj2p.json"}},{"package":{"name":"@openzeppelin/contracts-upgradeable","ecosystem":"npm","purl":"pkg:npm/%40openzeppelin/contracts-upgradeable"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.7.0"},{"fixed":"4.9.2"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2023/06/GHSA-wprv-93r4-jj2p/GHSA-wprv-93r4-jj2p.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N"}]}