Paymaster Contracts Audit | Tea-Fi | Halborn Audit Reports

Summary

100% of all REPORTED Findings have been addressed

About this report

Assessment Type

Assurance Assessment

Date of Engagement

October 27th, 2025 - October 31st, 2025

Source Code

paymaster-bc

Assessed Commit ID

c7fba27

Severity Breakdown

1Acknowledged
1Risk Accepted
7Solved
9All Findings

Critical0
High0
Medium3
- 2Solved
- 1Risk A.
Low3
- 3Solved
Informational3
- 1Ack.
- 2Solved

Summary#

Tea-Fi engaged Halborn to conduct a security assessment on their smart contracts beginning on October 27, 2025 and ending on October 30, 2025. The scope of this assessment was limited to the smart contracts provided to the Halborn team. Commit hashes and additional details are documented in the Scope section of this report.

TeaFi's NogaPaymaster is an ERC-4337 compatible smart contract that enables users to pay gas fees with ERC-20 tokens instead of native assets like ETH or MATIC. As part of NOGA’s EasyGas SaaS, it delivers secure, gasless transactions through EIP-712 signature validation, operator nonce protection, and precise post-operation token charging. With role-based access, pausability, and batch withdrawals, it ensures safety and flexibility. Its companion, CollectorSwapper, optionally converts collected tokens into a canonical token like USDC via Uniswap V3 without risking reverts, creating a seamless token-based gas abstraction system for Web3.

Assessment Summary#

Halborn was provided 4 days for the engagement and assigned 1 full-time security engineer to review the security of the smart contracts in scope. The engineer is a blockchain and smart contract security expert with advanced penetration testing and smart contract hacking skills, and deep knowledge of multiple blockchain protocols.

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 several areas for improvement to reduce both the likelihood and impact of potential risks, which were mostly addressed by the Tea-Fi team. The primary suggestions included:

Modify the calculation to round up the division result to ensure fair payment.
Instead of passing amountOutMin in the opaque data, the contract should use Uniswap V3's Quoter contract within postOpHandle().
Integrate On-Chain Price Oracles which fetches the current exchange rate at the moment of execution.
Wrap all external calls in try-catch and emit events on failure.
FOT tokens should be explicitly prevented.
Enforce a maximum allowed length for the tokens and amounts arrays in _withdrawTokensBatch().

Test Approach and Methodology#

Halborn performed a combination of manual code review and automated security testing to balance efficiency, timeliness, practicality, and accuracy in regard to the scope of this assessment. While manual testing is essential to uncover flaws in logic, process, and implementation, automated testing techniques enhance coverage of smart contracts and can quickly identify issues that do not follow security best practices.

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

Research into the architecture, purpose, and use of the platform.
Manual code review and walkthrough of the smart contracts to identify potential logic issues.
Manual testing of all core functions, including createCampaign, claim to validate expected behavior and identify edge-case vulnerabilities.
Local testing to simulate contract interactions and validate functional and security assumptions.
Local deployment and testing with Foundry.

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:paymaster-bc

(b) Assessed Commit ID:c7fba274c05bfaaddf49fffc305f90c5fecf6aca

11 files

contracts

11 files

components

5 files

ApproveManager.sol

solidity

EIP712Service.sol

solidity

StakeManager.sol

solidity

StorageCollectorSwapper.sol

solidity

ValidationModifiers.sol

solidity

errors

2 files

CollectorSwapperErrors.sol

solidity

PaymasterErrors.sol

solidity

interfaces

2 files

ICollectorSwapper.sol

solidity

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

45d393762125d4f7ee215fc1463844e9e4f7e733 5a93ca248d81e55517d38e1ba8a9953cdb8c32cf b8af8070200037ee43111f2bf52674dc3e233204 a8f4697bef122d33f676253d40185f80c1692770 a837a2a2623efaffaa04e294da985d2de3b22783 50b7396ecac066cc6a0967dc87aa1498f9bb8fe2 33d1ba98836026aac492343f58f22c192f9b8535

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

Assessment Summary & Findings Overview#

#	Title	Severity	Score	Status
HAL-01	Rounding Down in Token Fee Calculation Causes Underpayment	Medium	5.0	Solved11/04/2025
HAL-02	Strict Slippage Configuration Causes Swap Reverts	Medium	5.0	Solved11/05/2025
HAL-03	Exchange Rate Volatility Between Signing and Execution	Medium	5.0	Risk Accepted11/06/2025
HAL-04	withdrawTokensBatch() Lacks Zero-Amount Validation	Low	2.5	Solved11/04/2025
HAL-05	FOT (Fee-On-Transfer) Tokens can Cause Reverts and are Unsupported in PostOp Swaps	Low	2.5	Solved11/09/2025
HAL-06	Unbounded Loop in Batch Withdrawal	Low	2.5	Solved11/04/2025
HAL-07	postOp() Failures in Token Transfer are Silent	Informational	1.7	Acknowledged11/06/2025
HAL-08	Typo in Function Name _valdiatePostOpHandle	Informational	1.7	Solved11/04/2025
HAL-09	Inconsistent Solidity Version	Informational	1.7	Solved11/04/2025

Findings & Tech Details#

HAL-01Solved

Rounding Down in Token Fee Calculation Causes Underpayment

Medium

5.0AO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:N/D:N/Y:MAO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:N/D:N/Y:M

Description

Recommendation

Remediation Comment

Addressed in:

45d393762125d4f7ee215fc1463844e9e4f7e733

HAL-02Solved

Strict Slippage Configuration Causes Swap Reverts

Medium

5.0AO:A/AC:L/AX:L/R:N/S:U/C:N/A:M/I:N/D:N/Y:NAO:A/AC:L/AX:L/R:N/S:U/C:N/A:M/I:N/D:N/Y:N

Description

Recommendation

Remediation Comment

Addressed in:

5a93ca248d81e55517d38e1ba8a9953cdb8c32cf

HAL-03Risk Accepted

Exchange Rate Volatility Between Signing and Execution

Medium

5.0AO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:N/D:M/Y:NAO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:N/D:M/Y:N

Description

Recommendation

Remediation Comment

HAL-04Solved

withdrawTokensBatch() Lacks Zero-Amount Validation

Low

2.5AO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:L/D:N/Y:NAO:A/AC:L/AX:L/R:N/S:U/C:N/A:N/I:L/D:N/Y:N

Description

Recommendation

Remediation Comment

Addressed in:

b8af8070200037ee43111f2bf52674dc3e233204

HAL-05Solved

FOT (Fee-On-Transfer) Tokens can Cause Reverts and are Unsupported in PostOp Swaps

Low

2.5AO:A/AC:L/AX:L/R:N/S:U/C:N/A:L/I:N/D:N/Y:NAO:A/AC:L/AX:L/R:N/S:U/C:N/A:L/I:N/D:N/Y:N

Description

Recommendation

Remediation Comment

Addressed in:

a8f4697bef122d33f676253d40185f80c1692770

HAL-06Solved

Unbounded Loop in Batch Withdrawal

Low

2.5AO:A/AC:L/AX:L/R:N/S:U/C:N/A:L/I:N/D:N/Y:NAO:A/AC:L/AX:L/R:N/S:U/C:N/A:L/I:N/D:N/Y:N

Description

Recommendation

Remediation Comment

Addressed in:

a837a2a2623efaffaa04e294da985d2de3b22783

HAL-07Acknowledged

postOp() Failures in Token Transfer are Silent

Informational

1.7AO:A/AC:M/AX:L/R:N/S:U/C:N/A:N/I:L/D:N/Y:NAO:A/AC:M/AX:L/R:N/S:U/C:N/A:N/I:L/D:N/Y:N

Description

Recommendation

Remediation Comment

HAL-08Solved

Typo in Function Name _valdiatePostOpHandle

Informational

1.7AO:A/AC:M/AX:L/R:N/S:U/C:N/A:N/I:L/D:N/Y:NAO:A/AC:M/AX:L/R:N/S:U/C:N/A:N/I:L/D:N/Y:N

Description

Recommendation

Remediation Comment

Addressed in:

50b7396ecac066cc6a0967dc87aa1498f9bb8fe2

HAL-09Solved

Inconsistent Solidity Version

Informational

1.7AO:A/AC:M/AX:L/R:N/S:U/C:N/A:N/I:L/D:N/Y:NAO:A/AC:M/AX:L/R:N/S:U/C:N/A:N/I:L/D:N/Y:N

Description

Recommendation

Remediation Comment

Addressed in:

33d1ba98836026aac492343f58f22c192f9b8535

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.