Metalayer-Fetcher: Smart Contract Assessment Audit | Caldera

Summary

100% of all REPORTED Findings have been addressed

About this report

Assessment Type

Assurance Assessment

Date of Engagement

May 26th, 2025 - June 2nd, 2025

Source Code

metalayer-fetcher

Assessed Commit ID

b687425

Severity Breakdown

0Acknowledged
0Risk Accepted
3Solved
3All Findings

Critical0
High0
Medium1
- 1Solved
Low0
Informational2
- 2Solved

Introduction#

Caldera engaged Halborn to conduct a security assessment on their smart contracts beginning on May 26th, 2025 and ending on June 2nd, 2025. The security assessment was scoped to the smart contracts provided to Halborn. Commit hashes and further details can be found in the Scope section of this report.

The Caldera codebase in scope consists of the MetaERC20 smart contracts, a cross-chain token bridge built on top of the Metalayer/Hyperlane messaging protocol. It enables seamless transfer of ERC20 tokens between different blockchain networks while maintaining token supply integrity and providing security controls for high-value transfers.

Assessment Summary#

Halborn was provided 7 days for the engagement and assigned a full-time security engineer to review the security of the smart contracts in scope.

The purpose of the assessment is to:

Identify potential security issues within the smart contracts.
Ensure that smart contract functionality operates as intended.

In summary, Halborn identified some improvements to reduce the likelihood and impact of risks, which were completely addressed by Caldera. The main one was the following:

Implement a functionality to disallow transfers marked as executed during emergency to be executed again

Test Approach and Methodology#

Halborn performed a manual review of the code. Manual testing is great to uncover flaws in logic, process, and implementation.

The following phases and associated tools were used throughout the term of the assessment:

Research into architecture, purpose and use of the platform.
Smart contract manual code review and walkthrough to identify any logic issue.
Thorough assessment of safety and usage of critical Solidity variables and functions in scope that could led to arithmetic related vulnerabilities.

Risk Methodology#

Every vulnerability and issue observed by Halborn is ranked based on two sets of Metrics and a Severity Coefficient. This system is inspired by the industry standard Common Vulnerability Scoring System.

The two Metric sets are: Exploitability and Impact. Exploitability captures the ease and technical means by which vulnerabilities can be exploited and Impact describes the consequences of a successful exploit.

The Severity Coefficients is designed to further refine the accuracy of the ranking with two factors: Reversibility and Scope. These capture the impact of the vulnerability on the environment as well as the number of users and smart contracts affected.

The final score is a value between 0-10 rounded up to 1 decimal place and 10 corresponding to the highest security risk. This provides an objective and accurate rating of the severity of security vulnerabilities in smart contracts.

The system is designed to assist in identifying and prioritizing vulnerabilities based on their level of risk to address the most critical issues in a timely manner.

4.1 EXPLOITABILITY

Attack Origin (AO):

Captures whether the attack requires compromising a specific account.

Attack Cost (AC):

Captures the cost of exploiting the vulnerability incurred by the attacker relative to sending a single transaction on the relevant blockchain. Includes but is not limited to financial and computational cost.

Attack Complexity (AX):

Describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability. Includes but is not limited to macro situation, available third-party liquidity and regulatory challenges.

Metrics:

EXPLOITABILITY METRIC ( $m_e$ )	METRIC VALUE	NUMERICAL VALUE
Attack Origin (AO)	Arbitrary (AO:A)	1
Attack Origin (AO)	Specific (AO:S)	0.2
Attack Cost (AC)	Low (AC:L)	1
	Medium (AC:M)	0.67
	High (AC:H)	0.33
Attack Complexity (AX)	Low (AX:L)	1
	Medium (AX:M)	0.67
	High (AX:H)	0.33

Exploitability

E

is calculated using the following formula:

$E = \prod m_e$

4.2 IMPACT

Confidentiality (C):

Measures the impact to the confidentiality of the information resources managed by the contract due to a successfully exploited vulnerability. Confidentiality refers to limiting access to authorized users only.

Integrity (I):

Measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of data stored and/or processed on-chain. Integrity impact directly affecting Deposit or Yield records is excluded.

Availability (A):

Measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. This metric refers to smart contract features and functionality, not state. Availability impact directly affecting Deposit or Yield is excluded.

Deposit (D):

Measures the impact to the deposits made to the contract by either users or owners.

Yield (Y):

Measures the impact to the yield generated by the contract for either users or owners.

Metrics:

IMPACT METRIC ( $m_I$ )	METRIC VALUE	NUMERICAL VALUE
Confidentiality (C)	None (C:N)	0
	Low (C:L)	0.25
	Medium (C:M)	0.5
	High (C:H)	0.75
	Critical (C:C)	1
Integrity (I)	None (I:N)	0
	Low (I:L)	0.25
	Medium (I:M)	0.5
	High (I:H)	0.75
	Critical (I:C)	1
Availability (A)	None (A:N)	0
	Low (A:L)	0.25
	Medium (A:M)	0.5
	High (A:H)	0.75
	Critical (A:C)	1
Deposit (D)	None (D:N)	0
	Low (D:L)	0.25
	Medium (D:M)	0.5
	High (D:H)	0.75
	Critical (D:C)	1
Yield (Y)	None (Y:N)	0
	Low (Y:L)	0.25
	Medium (Y:M)	0.5
	High (Y:H)	0.75
	Critical (Y:C)	1

Impact

I

is calculated using the following formula:

$I = max(m_I) + \frac{\sum{m_I} - max(m_I)}{4}$

4.3 SEVERITY COEFFICIENT

Reversibility (R):

Describes the share of the exploited vulnerability effects that can be reversed. For upgradeable contracts, assume the contract private key is available.

Scope (S):

Captures whether a vulnerability in one vulnerable contract impacts resources in other contracts.

Metrics:

SEVERITY COEFFICIENT ( $C$ )	COEFFICIENT VALUE	NUMERICAL VALUE
Reversibility ( $r$ )	None (R:N)	1
	Partial (R:P)	0.5
	Full (R:F)	0.25
Scope ( $s$ )	Changed (S:C)	1.25
Scope ( $s$ )	Unchanged (S:U)	1

Severity Coefficient

C

is obtained by the following product:

$C = rs$

The Vulnerability Severity Score

S

is obtained by:

$S = min(10, EIC * 10)$

The score is rounded up to 1 decimal places.

Critical	High	Medium	Low	Informational
9 - 10	7 - 8.9	4.5 - 6.9	2 - 4.4	0 - 1.9

Scope#

(a) Repository:metalayer-fetcher

(b) Assessed Commit ID:b6874250ebb15f734d5a6145679637f7fae5bfb5

5 files

MetaERC20Base.sol

solidity

MetaERC20Hub.sol

solidity

MetaERC20Message.sol

solidity

MetaERC20Spoke.sol

solidity

MetaERC20Types.sol

solidity

Out-of-Scope:Third party dependencies and economic attacks.

7e4c282770b047dd485d1ce0dbdf0c5fbf6d6494 https://github.com/ConstellationCrypto/metalayer-fetcher/pull/53 https://github.com/ConstellationCrypto/metalayer-fetcher/pull/55

Out-of-Scope: New features/implementations after the remediation commit IDs.

Assessment Summary & Findings Overview#

#	Title	Severity	Score	Status
HAL-01	Emergency functions do not consider a possible message arrival in the future	Medium	6.3	Solved05/28/2025
HAL-02	Floating pragma version	Informational	0.0	Solved07/08/2025
HAL-03	Redundant checks in token recovery functions	Informational	0.0	Solved07/08/2025

Findings & Tech Details#

HAL-01Solved

Emergency functions do not consider a possible message arrival in the future

Medium

6.3AO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:M/D:M/Y:NAO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:M/D:M/Y:N

Description

Recommendation

Remediation Comment

Addressed in:

7e4c282770b047dd485d1ce0dbdf0c5fbf6d6494

HAL-02Solved

Floating pragma version

Informational

0.0AO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:N/D:N/Y:NAO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:N/D:N/Y:N

Description

Recommendation

Remediation Comment

Addressed in:

https://github.com/ConstellationCrypto/metalayer-fetcher/pull/53

HAL-03Solved

Redundant checks in token recovery functions

Informational

0.0AO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:N/D:N/Y:NAO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:N/D:N/Y:N

Description

Recommendation

Remediation Comment

Addressed in:

https://github.com/ConstellationCrypto/metalayer-fetcher/pull/55

Disclaimer#

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.