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Cosmos EVM - TAC

Prepared by:

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HALBORN

Last Updated 06/26/2025

Date of Engagement: June 16th, 2025 - June 16th, 2025

Summary

100% of all REPORTED Findings have been addressed

All findings

1

Critical

0

High

0

Medium

0

Low

1

Informational

0

Table of Contents

1. Introduction

TAC engaged Halborn to perform a security assessment of their smart contracts on June 16th, 2025. This assessment focused on specific changes made to a Cosmos module provided to the Halborn team. Commit hashes and additional details are available in the Scope section of this report.


TAC is a Layer 1 introducing a novel TON-Adapter that enables Ethereum dApps to access Telegram’s users, and is also TON’s first EVM-equivalent extension.

2. Assessment Summary

The Halborn team assigned two full-time security engineers to evaluate the security of the merge requests. These engineers are experts in blockchain and smart contract security, with advanced skills in penetration testing, smart contract auditing, and extensive knowledge of multiple blockchain protocols.

The objectives of this assessment were to:

    • Verify that the Golang components function as intended.

    • Identify potential security vulnerabilities within the Cosmos application.

 

In summary, Halborn identified one improvement to reduce the likelihood and impact of risks, which was addressed by the TAC team:

    • Implement checked conversion to prevent panic reverts.

3. Test Approach and Methodology

Halborn employed a combination of manual and automated security testing to balance efficiency, timeliness, practicality, and accuracy within the scope of the custom modules. Manual testing was used to uncover logical, procedural, and implementation flaws, while automated testing enhanced coverage and quickly identified deviations from security best practices. The following phases and tools were utilized during the assessment:

    • Research into architecture and purpose.

    • Static analysis of the scoped repository and imported functions using tools such as staticcheck, gosec, unconvert, codeql, ineffassign, and semgrep.

    • Manual assessment to identify security vulnerabilities within the codebase.

    • Verification of codebase correctness.

    • Dynamic analysis of files and modules within scope.

4. Caveats

CosmosEVM security assessment is limited to the files directly affected by the Pull Request listed in the Sources section. Only changes introduced or modified in this comparison were considered; any pre-existing vulnerabilities or issues outside these specific files are beyond the scope of this review. Additionally, the audit does not cover dependencies, configuration files, or runtime environments. Therefore, findings and recommendations apply solely to the code and files added, removed, or modified in this branch comparison.

5. 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.

5.1 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

5.2 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 (I:N)
Low (I:L)
Medium (I:M)
High (I:H)
Critical (I: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}

5.3 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

6. SCOPE

Files and Repository
(a) Repository: evm
(b) Assessed Commit ID: f683909
(c) Items in scope:
Out-of-Scope: Third party dependencies and economic attacks.
Remediation Commit ID:
Out-of-Scope: New features/implementations after the remediation commit IDs.

7. Assessment Summary & Findings Overview

Critical

0

High

0

Medium

0

Low

1

Informational

0

Security analysisRisk levelRemediation Date
Possible uint256 Overflow Panic LowSolved - 06/24/2025

8. Findings & Tech Details

8.1 Possible uint256 Overflow Panic

//

Low

Description

In precompiles/staking/tx.go::Delegate, uint256.MustFromBig(scaledAmt) panics if scaledAmt > 2^{256}-1. Triggering this condition would require supplying at least 1.15\times10^{65} native tokens (assuming a 6-decimal denomination), which far exceeds any realistic total supply:


// Scale the amount to 18 decimals for the EVM balance change entry
scaledAmt := evmtypes.ConvertAmountTo18DecimalsBigInt(msg.Amount.Amount.BigInt())
p.SetBalanceChangeEntries(cmn.NewBalanceChangeEntry(delHexAddr, uint256.MustFromBig(scaledAmt), cmn.Sub))

BVSS
Recommendation

The condition is practically unreachable and cannot be exploited as a denial-of-service vector. However, replacing the Must… helper with a checked conversion is a low-cost hardening measure:

scaled, overflow := uint256.FromBig(scaledAmt)
if overflow {
    return nil, fmt.Errorf("delegate amount too large for uint256")
}
p.SetBalanceChangeEntries(cmn.NewBalanceChangeEntry(delHexAddr, scaled, cmn.Sub))

Remediation Comment

SOLVED: The suggested mitigation was implemented.

Remediation Hash
https://github.com/TacBuild/evm/commit/16b1cdbeee3909a6271988bbc54b907c5d64762b

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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