Prepared by:
HALBORN
Last Updated 10/20/2025
Date of Engagement: January 9th, 2023 - March 8th, 2023
100% of all REPORTED Findings have been addressed
All findings
5
Critical
1
High
0
Medium
0
Low
1
Informational
3
MatterLabs zkSync Era is a Layer 2 blockchain protocol that eliminates Ethereum’s inherent congestion with zero knowledge proofs. Matter Labs' creation is on a mission to accelerate the mass adoption of crypto for personal sovereignty. It is designed to unlock the full potential of trustless blockchain technology while scaling the core values of Ethereum.
MatterLabs engaged Halborn to conduct a security audit on their zero knowledge circuits and the verifier, beginning on 2023-01-09 and ending on 2023-03-08. The security assessment was scoped to the circuits provided to the Halborn team.
The team at Halborn was provided two months for the engagement and assigned a full-time security engineer to audit the security of the zero knowledge circuits and the verifier. The security engineer is a blockchain, smart-contract and ZK security expert with advanced penetration testing, smart-contract hacking, and deep knowledge of multiple blockchain protocols.
The purpose of this audit to achieve the following:
Ensure that the circuits operate as intended.
Identify potential security issues within the circuits.
Ensure that the verifier operate as intended.
Identify potential security issues within the verifier contracts.
In summary, Halborn identified some security risks that were mostly addressed by the MatterLabs team.
Halborn performed a combination of manual and automated security testing to balance efficiency, timeliness, practicality, and accuracy in regard to the scope of this audit. While manual testing is recommended to uncover flaws in logic, process, and implementation; automated testing techniques help enhance coverage of the bridge code and can quickly identify items that do not follow security best practices. The following phases and associated tools were used throughout the term of the audit:
Research into architecture and purpose.
Smart contract manual code review and walkthrough.
Circuit manual code review and walkthrough.
Graphing out functionality and circuit logic/connectivity/functions. (cargo-deps)
Manual code review of common Rust security vulnerabilities.
Manual code review of specific zero knowledge security vulnerabilities.
Scanning of circuits files for unsafe Rust code usage. (cargo-geiger)
Static Analysis of security for scoped circuits, and imported functions. (cargo-audit)
1. IN-SCOPE:
The security assessment was scoped to the following zero knowledge circuits:
/src/vm/*
/src/glue/sort_decommitments_requests/*
/src/glue/code_unpacker_sha256/*
/src/glue/demux_log_queue/*
/src/precompiles/keccak256.rs
/src/precompiles/sha256.rs
/src/glue/ecrecover_circuit/*
/src/glue/ram_permutation/*
/src/glue/storage_validity_by_grand_product/*
/src/glue/storage_application/*
/src/glue/pub_data_hasher/*
/src/glue/log_sorter/*
/src/glue/merkleize_l1_messages/*
/src/scheduler/*
/src/circuit_structures/*
/src/data_structures/*
/src/inputs/*
/src/recursion/*
/src/traits/*
/src/secp256k1/*
/src/utils.rs
Commit ID : 014e674916058e31725d6e92439fa5ff14e6677e
And the verifier:
/zksync/Verifier.sol
/zksync/Plonk4VerifierWithAccessToDNext.sol
/zksync/libraries/PairingsBn254.sol
/zksync/libraries/TranscriptLib.sol
Commit ID : fc7e86a3df404acb88d86502c944c0630a7ed288
2. REMEDIATION PR/COMMITS:
Fix Commit ID (HAL-01) : 5109e0768c7de799f87ec67bf40b6a544cca4e4e
Fix Commit ID (HAL-02) : b0a79356613655bddccaab3b89dbf1142b5483fb
Fix Commit ID (HAL-03): 06c2e76546369fb112d8ac14fb5388154857435b
| EXPLOITABILITY METRIC () | METRIC VALUE | NUMERICAL VALUE |
|---|---|---|
| Attack Origin (AO) | Arbitrary (AO:A) Specific (AO:S) | 1 0.2 |
| Attack Cost (AC) | Low (AC:L) Medium (AC:M) High (AC:H) | 1 0.67 0.33 |
| Attack Complexity (AX) | Low (AX:L) Medium (AX:M) High (AX:H) | 1 0.67 0.33 |
| IMPACT METRIC () | METRIC VALUE | NUMERICAL VALUE |
|---|---|---|
| Confidentiality (C) | None (C:N) Low (C:L) Medium (C:M) High (C:H) Critical (C:C) | 0 0.25 0.5 0.75 1 |
| Integrity (I) | None (I:N) Low (I:L) Medium (I:M) High (I:H) Critical (I:C) | 0 0.25 0.5 0.75 1 |
| Availability (A) | None (A:N) Low (A:L) Medium (A:M) High (A:H) Critical (A:C) | 0 0.25 0.5 0.75 1 |
| Deposit (D) | None (D:N) Low (D:L) Medium (D:M) High (D:H) Critical (D:C) | 0 0.25 0.5 0.75 1 |
| Yield (Y) | None (Y:N) Low (Y:L) Medium (Y:M) High (Y:H) Critical (Y:C) | 0 0.25 0.5 0.75 1 |
| SEVERITY COEFFICIENT () | COEFFICIENT VALUE | NUMERICAL VALUE |
|---|---|---|
| Reversibility () | None (R:N) Partial (R:P) Full (R:F) | 1 0.5 0.25 |
| Scope () | Changed (S:C) Unchanged (S:U) | 1.25 1 |
| Severity | Score Value Range |
|---|---|
| Critical | 9 - 10 |
| High | 7 - 8.9 |
| Medium | 4.5 - 6.9 |
| Low | 2 - 4.4 |
| Informational | 0 - 1.9 |
Critical
1
High
0
Medium
0
Low
1
Informational
3
| Security analysis | Risk level | Remediation Date |
|---|---|---|
| CIRCUIT NOT PROPERLY WORKING WHEN USING SHARD ID > 0 | Critical | Solved - 04/03/2023 |
| HEAD STATE NOT ENFORCED TO BE ZERO | Low | Solved - 04/03/2023 |
| UNUSED CIRCUIT FUNCTIONALITY | Informational | Solved - 04/03/2023 |
| QUEUE NOT ENFORCED TO BE EMPTY RIGHT AFTER POPPING ALL ELEMENTS | Informational | Acknowledged - 04/03/2023 |
| UNNEEDED INITIALIZATION OF UINT256 VARIABLES | Informational | Acknowledged - 04/03/2023 |
//Critical
//Low
//Informational
//Informational
//Informational
Halborn strongly recommends conducting a follow-up assessment of the project either within six months or immediately following any material changes to the codebase, whichever comes first. This approach is crucial for maintaining the project’s integrity and addressing potential vulnerabilities introduced by code modifications.
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