OpenZeppelin Contracts's MerkleProof multiproofs may allow proving arbitrary leaves for specific trees

Summary

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. 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 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. 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. The problem has been patched in version 4.9.2. Some 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.

Timeline

1. Jun 16, 2023, 10:13 PM UTCCVE published
2. Dec 16, 2024, 6:35 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Dec 16, 2024, 6:35 PM UTCRecord last updated

Affected versions

• OpenZeppelin openzeppelin-contracts

  From 4.7.0 · fixed in 4.9.2

• @openzeppelin/contractsnpm

  From 4.7.0 · fixed in 4.9.2

• @openzeppelin/contracts-upgradeablenpm

  From 4.7.0 · fixed in 4.9.2

References 3