CVE-2023-34459 OpenZeppelin Contracts's MerkleProof multiproofs may allow proving arbitrary leaves for specific trees

Medium 5.3 Published 16 Jun 2023 Updated 16 Dec 2024

Attackers can forge valid Merkle multiproofs for specific tree structures, allowing unauthorized state changes in smart contracts using affected OpenZeppelin functions.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2023-34459?

CVE-2023-34459 is a medium-severity vulnerability in openzeppelin-contracts, published on 16 Jun 2023. Any signed-in user can exploit it over the network, with no action from the victim.

Official 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.

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.

Weakness: CWE-354

Which versions are affected by CVE-2023-34459?

4 open source packages ship an affected version, including @openzeppelin/contracts and @openzeppelin/contracts-upgradeable. It affects 2 products.

Package	Affected	Fixed in
`@openzeppelin/contracts` npm	From `4.7.0`	`4.9.2`
`@openzeppelin/contracts` npm	From `4.7.0`	`4.9.2`
`@openzeppelin/contracts-upgradeable` npm	From `4.7.0`	`4.9.2`
`@openzeppelin/contracts-upgradeable` npm	From `4.7.0`	`4.9.2`

Products include Openzeppelin Contracts, Openzeppelin Contracts Upgradeable.

How do I fix CVE-2023-34459?

Upgrade @openzeppelin/contracts to 4.9.2 or later.

Is CVE-2023-34459 being exploited?

There is no known exploitation of CVE-2023-34459 in the wild and no public exploit code.

Sources

Also known as GHSA-wprv-93r4-jj2p.