Headline
CVE-2023-34459: Merge pull request from GHSA-wprv-93r4-jj2p · OpenZeppelin/openzeppelin-contracts@4d2383e
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.
@@ -1,11 +1,8 @@ require(‘@openzeppelin/test-helpers’);
const { expectRevert } = require(‘@openzeppelin/test-helpers’); const { expect } = require(‘chai’); const { MerkleTree } = require(‘merkletreejs’); const keccak256 = require(‘keccak256’);
const { expect } = require(‘chai’);
const MerkleProof = artifacts.require(‘$MerkleProof’);
contract('MerkleProof’, function () { Expand Down Expand Up @@ -176,5 +173,28 @@ contract('MerkleProof’, function () { expect(await this.merkleProof.$multiProofVerify([root], [], root, [])).to.equal(true); expect(await this.merkleProof.$multiProofVerifyCalldata([root], [], root, [])).to.equal(true); });
it('reverts processing manipulated proofs with a zero-value node at depth 1’, async function () { // Create a merkle tree that contains a zero leaf at depth 1 const leaves = [keccak256(‘real leaf’), Buffer.alloc(32, 0)]; const merkleTree = new MerkleTree(leaves, keccak256, { sortPairs: true });
const root = merkleTree.getRoot();
// Now we can pass any ** malicious ** fake leaves as valid! const maliciousLeaves = ['some’, 'malicious’, ‘leaves’].map(keccak256).sort(Buffer.compare); const maliciousProof = [leaves[0], leaves[0]]; const maliciousProofFlags = [true, true, false];
await expectRevert( this.merkleProof.$multiProofVerify(maliciousProof, maliciousProofFlags, root, maliciousLeaves), 'MerkleProof: invalid multiproof’, );
await expectRevert( this.merkleProof.$multiProofVerifyCalldata(maliciousProof, maliciousProofFlags, root, maliciousLeaves), 'MerkleProof: invalid multiproof’, ); }); }); });
Related news
### Impact When 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. 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 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. 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](https://github.com/OpenZeppelin/merkle-tree) library are safe. ### Patches The problem has be...