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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N

EPSS

• CVE-2023-34459: 0.37% estimated exploitation activity in the next 30 days; percentile 31.06 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 library are safe. Patches The problem has been patched in 4.9.2. Workarounds If you are using multiproofs: When…

Published by the source

19 Jun 2023, 19:46 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:27 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-wprv-93r4-jj2p

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-wprv-93r4-jj2p

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# Patch Next advisory brief: CVE-2023-34459

Advisory: OpenZeppelin Contracts using MerkleProof multiproofs may allow proving arbitrary leaves for specific trees
IDs: CVE-2023-34459, GHSA-wprv-93r4-jj2p
Record: https://patchnext.com/advisories/cve-2023-34459 (revision 2, source checked 26 Oct 2026, 12:27 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @openzeppelin/contracts 4.9.2; @openzeppelin/contracts-upgradeable 4.9.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @openzeppelin/contracts: affected >= 4.7.0, < 4.9.2; fixed in 4.9.2
- npm @openzeppelin/contracts-upgradeable: affected >= 4.7.0, < 4.9.2; fixed in 4.9.2

## Suggested inspection (read-only)
- `npm ls @openzeppelin/contracts --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- `npm ls @openzeppelin/contracts-upgradeable --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @openzeppelin/contracts, @openzeppelin/contracts-upgradeable.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-wprv-93r4-jj2p (OSV record GHSA-wprv-93r4-jj2p lists affected ranges: npm @openzeppelin/contracts >=4.7.0 =4.7.0 <4.9.2 (fixed))
- Verified: https://github.com/advisories/GHSA-wprv-93r4-jj2p (GitHub-reviewed advisory GHSA-wprv-93r4-jj2p lists affected ranges: npm @openzeppelin/contracts >=4.7.0 =4.7.0 <4.9.2)

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