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Bridge Contracts - Casper Association

Prepared by:

Halborn Logo

HALBORN

Last Updated Unknown date

Date of Engagement: June 17th, 2024 - July 17th, 2024

Summary

100% of all REPORTED Findings have been addressed

All findings

9

Critical

0

High

0

Medium

0

Low

6

Informational

3

Table of Contents

1. Introduction

Allbridge engaged Halborn to conduct a security assessment of the Bridge and ERC20 contracts, beginning on June 17th, 2024 and ending on July 17th, 2024. This security assessment was scoped to the smart contracts in the bridge-casper-contract GitHub repository.

Allbridge is a simple and reliable tool for moving assets between different blockchain networks. It contributes to a more connected blockchain world by enabling easy and fast transfers, allowing assets to move quickly, similar to normal transactions on any blockchain. Allbridge also offers the flexibility to choose how to send and receive tokens, whether they are native to the blockchain or wrapped versions.

2. Assessment Summary

The team at Halborn assigned a full-time security engineer to verify the security of the smart contracts. The security engineer is a blockchain and smart-contract security expert with advanced penetration testing, smart-contract hacking, and deep knowledge of multiple blockchain protocols.

The purpose of this assessment is to:

    • Ensure that smart contract functions operate as intended.

    • Identify potential security issues with the smart contracts.


In summary, Halborn identified some improvements to reduce the likelihood and impact of risks, which were acknowledged by the Allbridge team. The main ones are the following: 

    • The status of the token should be checked before performing any operations.

    • The access permission of the constructor entry point should be changed to Groups since a user group is created.

    • The fee rate should be checked to ensure it is lower than 100% or under a maximum threshold to avoid unintended errors.

    • The ERC20 contract should provide a mechanism for upgrades if needed.

    • The lock_id should be validated in conjunction with the transaction sender's address to avoid forged lock requests.

    • Ownership should be transferred in a two-step process to avoid lossing the control of the contract.

3. Test Approach and Methodology

Halborn performed a combination of the manual view of the code and automated security testing to balance efficiency, timeliness, practicality, and accuracy regarding the scope of the smart contract assessment. While manual testing is recommended to uncover flaws in logic, process, and implementation, automated testing techniques help enhance the coverage of smart contracts. They can quickly identify items that do not follow security best practices. The following phases and associated tools were used throughout the term of the assessment:

    • Research into architecture, purpose, and use of the platform.

    • Manual code read and walk through.

    • Manual Assessment of use and safety for the critical Rust variables and functions in scope to identify any arithmetic related vulnerability classes.

    • Cross contract call controls.

    • Architecture related logical controls.

    • Scanning of Rust files for vulnerabilities (cargo audit)

    • Integration testing using the Casper Engine Test Support.

    • Tesnet deployment and comprehensive review of transactions through the CPSR live explorer.

4. 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 (mem_e)METRIC VALUENUMERICAL 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
Exploitability EE is calculated using the following formula:

E=∏meE = \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 (mIm_I)METRIC VALUENUMERICAL 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
Impact II is calculated using the following formula:

I=max(mI)+∑mI−max(mI)4I = 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 (CC)COEFFICIENT VALUENUMERICAL VALUE
Reversibility (rr)None (R:N)
Partial (R:P)
Full (R:F)		1
0.5
0.25
Scope (ss)Changed (S:C)
Unchanged (S:U)		1.25
1
Severity Coefficient CC is obtained by the following product:

C=rsC = rs

The Vulnerability Severity Score SS is obtained by:

S=min(10,EIC∗10)S = min(10, EIC * 10)

The score is rounded up to 1 decimal places.
SeverityScore Value Range
Critical9 - 10
High7 - 8.9
Medium4.5 - 6.9
Low2 - 4.4
Informational0 - 1.9

5. SCOPE

REPOSITORY
(a) Repository: bridge-casper-contract
(b) Assessed Commit ID: https://github.com/allbridge-io/bridge-casper-contract/tree/2a01c796af120eb6f86cd8b71575bfc4dd25c087
(c) Items in scope:
  • contracts/bridge
  • contracts/erc20
  • common/bridge_types
↓ Expand ↓
Out-of-Scope: Third party dependencies, economic attacks.
Out-of-Scope: New features/implementations after the remediation commit IDs.

6. Assessment Summary & Findings Overview

Critical

0

High

0

Medium

0

Low

6

Informational

3

Security analysisRisk levelRemediation Date
Unlock operation could be done on disabled tokensLowRisk Accepted
Incorrect access permissions in constructor entry pointLowRisk Accepted
Fee rate not validatedLowRisk Accepted
Lack of contract upgrade capabilityLowRisk Accepted
Potential lock ID forgery leading to DoSLowRisk Accepted
Owneship transfer in one stepLowRisk Accepted
Compliance with Casper Fungible Token Standard (CEP-18)InformationalAcknowledged
Redundant codeInformationalAcknowledged
Missing argument on entry pointInformationalAcknowledged

7. Findings & Tech Details

7.1 Unlock operation could be done on disabled tokens

//

Low

Description
BVSS
Recommendation

7.2 Incorrect access permissions in constructor entry point

//

Low

Description
BVSS
Recommendation

7.3 Fee rate not validated

//

Low

Description
BVSS
Recommendation

7.4 Lack of contract upgrade capability

//

Low

Description
BVSS
Recommendation

7.5 Potential lock ID forgery leading to DoS

//

Low

Description
BVSS
Recommendation

7.6 Owneship transfer in one step

//

Low

Description
BVSS
Recommendation

7.7 Compliance with Casper Fungible Token Standard (CEP-18)

//

Informational

Description
BVSS
Recommendation

7.8 Redundant code

//

Informational

Description
BVSS
Recommendation

7.9 Missing argument on entry point

//

Informational

Description
BVSS
Recommendation

8. Automated Testing

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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Bridge Contracts

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