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DestChainConfigV2 to Onramp- PR 287 - Chainlink Labs

Prepared by:

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HALBORN

Last Updated 09/25/2025

Date of Engagement: September 8th, 2025 - September 12th, 2025

Summary

100% of all REPORTED Findings have been addressed

All findings

7

Critical

0

High

0

Medium

0

Low

1

Informational

6

Table of Contents

1. Introduction

Chainlink Labs engaged Halborn to conduct a security assessment of several packages for the Aptos blockchain, beginning on September 8th, 2025, and ending on September 12th, 2025. This security assessment focused on the smart contracts within the chainlink-aptos GitHub repository; commit hashes and further details can be found in the Scope section of this report.


The engagement was performed to validate that the V2 migration and configuration changes are upgrade-safe and to identify functional and security issues introduced by the change.

2. Assessment Summary

The team at Halborn assigned one 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 partially addressed by the Chainlink team. The main ones were the following:

    • Provide explicit router_state_address values as migration inputs for each destination. Alternatively, ensure ccip_send is gated to return a clear "not configured" error until a non-zero, non-state-address value is set.

    • Impose a reasonable upper bound on fee_tokens.length() or provide documented batching guidance and tooling to process withdrawals in smaller chunks.

    • Use error::permission_denied(E_MUST_BE_CALLED_BY_ROUTER) instead of error::invalid_argument(...) for router authorization checks in both V1 and V2 ccip_send.


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 the architecture, purpose, and use of the platform.

    • Manual code review and walkthrough.

    • Manual assessment of the critical Move variables and functions in scope to identify any vulnerability classes related to arithmetic or logic.

    • Cross-contract call controls.

    • Logical controls related to the platform architecture.

    • Review unit tests.


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: chainlink-aptos
(b) Assessed Commit ID: https://github.com/smartcontractkit/chainlink-aptos/pull/287/commits/f0d729b15a030e08e376fb568d70c36dde3f8830
(c) Items in scope:
  • contracts/ccip/ccip_onramp/sources/onramp.move
Out-of-Scope: Third party dependencies and economic attacks.
Remediation Commit ID:
Out-of-Scope: New features/implementations after the remediation commit IDs.

6. Assessment Summary & Findings Overview

Critical

0

High

0

Medium

0

Low

1

Informational

6

Security analysisRisk levelRemediation Date
Post-migration default router_state_address disables sendsLowSolved - 09/22/2025
Unbounded input size in withdraw_fee_tokens can lead to gas-heavy callsInformationalAcknowledged - 09/22/2025
Overly permissive error classes for router authorization failuresInformationalSolved - 09/22/2025
No non-zero checks for router/router_state_address on updatesInformationalAcknowledged - 09/22/2025
Permissionless fee withdrawal enables griefing/spam and timing manipulationInformationalAcknowledged - 09/22/2025
Allowlist admin can be set to the zero addressInformationalAcknowledged - 09/22/2025
Fee withdrawal occurs prior to router/allowlist authorizationInformationalAcknowledged - 09/22/2025

7. Findings & Tech Details

7.1 Post-migration default router_state_address disables sends

//

Low

Description

After migrating to V2 (migrate_dest_chain_configs_to_v2), each DestChainConfigV2 is created with router_state_address set to the onramp state address (get_state_address_internal()).


In ccip_send, authorization requires dest_chain_config_v2.router_state_address == signer::address_of(router). Unless admins promptly update router_state_address per destination via apply_dest_chain_config_updates_v2, all sends will fail, effectively causing a liveness outage for that destination.


This is especially risky if migration is executed in production without a tightly coordinated follow-up.

BVSS
Recommendation

Provide explicit router_state_address values as migration inputs for each destination. Alternatively, ensure ccip_send is gated to return a clear "not configured" error until a non-zero, non-state-address value is set.

Remediation Comment

SOLVED: The Chainlink team solved this issue by updating migration to accept per‑destination router module addresses and, for each chain, set DestChainConfigV2.router to the provided module address while mapping the prior V1 router to router_state_address.

Remediation Hash
https://github.com/smartcontractkit/chainlink-aptos/pull/287/commits/2af7d92e7bcb1028c185f9edd56b7977120f688c

7.2 Unbounded input size in withdraw_fee_tokens can lead to gas-heavy calls

//

Informational

Description

The withdraw_fee_tokens function accepts an arbitrarily long fee_tokens vector, performing per‑token object checks and balance reads. Very large inputs can be operationally expensive and risk exceeding gas budgets.

BVSS
Recommendation

Impose a reasonable upper bound on fee_tokens.length() or provide documented batching guidance and tooling to process withdrawals in smaller chunks.

Remediation Comment

ACKNOWLEDGED: The Chainlink team acknowledged this finding.

7.3 Overly permissive error classes for router authorization failures

//

Informational

Description

Router authorization failures in ccip_send are reported using error::invalid_argument(E_MUST_BE_CALLED_BY_ROUTER) instead of error::permission_denied. As a result, telemetry is obscured, incident response and monitoring rules that depend on error domains are complicated, and the semantic distinction between caller errors and access violations is weakened.

BVSS
Recommendation

Replace error::invalid_argument(E_MUST_BE_CALLED_BY_ROUTER) with error::permission_denied(E_MUST_BE_CALLED_BY_ROUTER) for both V1 and V2 router authorization checks in ccip_send. Keep E_SENDER_NOT_ALLOWED under permission_denied and align future authorization checks to use permission_denied consistently.

Remediation Comment

SOLVED: The Chainlink team solved this issue in the specified commit ID.

Remediation Hash
https://github.com/smartcontractkit/chainlink-aptos/pull/287/commits/072d29094f098d884dd437276dd77cbe2bd1afb6

7.4 No non-zero checks for router/router_state_address on updates

//

Informational

Description

apply_dest_chain_config_updates and apply_dest_chain_config_updates_v2 are allowed to be configured with the zero address for router or router_state_address. If a destination is configured with the zero address, ccip_send becomes uncallable for that destination; only the 0x0 signer is accepted. This behavior can serve as a soft-disable, but it may be applied accidentally and be difficult to diagnose.

BVSS
Recommendation

Treat zero as an explicit disable. Accordingly:

  • (a) emit a dedicated “destination disabled” event, and

  • (b) require an optional, separate “disable” action to prevent accidental misconfiguration.


Remediation Comment

ACKNOWLEDGED: The Chainlink team acknowledged this finding but opted not to implement the change in order to maintain alignment with their EVM implementation.

7.5 Permissionless fee withdrawal enables griefing/spam and timing manipulation

//

Informational

Description

The withdraw_fee_tokens(fee_tokens) function is permissionless. Withdrawals of the module's fee balances to the configured fee_aggregator can be triggered by any account.


Although funds are not placed at risk (they are always forwarded to the aggregator), the following impacts can be caused:

  • Unexpected withdrawal timing can be forced, causing operational disruption, and

  • FeeTokenWithdrawn events can be spammed, cluttering monitoring and logs.


BVSS
Recommendation

Either (a) access should be restricted to the owner or an aggregator, or (b) permissionless access should be retained with additional mitigations: per-token cooldowns, rate limiting, an explicit operator-intent mechanism (for example, a boolean flag enabling public withdrawals), and more descriptive events.

Remediation Comment

ACKNOWLEDGED: The Chainlink team acknowledged this finding.

7.6 Allowlist admin can be set to the zero address

//

Informational

Description

The set_dynamic_config_internal function allows the allowlist_admin to be set to the zero address (0x0). When that assignment occurs, allowlist updates are restricted to the contract owner and the allowlist admin role is rendered effectively disabled. While this may be intended to implement a "no-admin" mode, an unintended assignment may impede operational flexibility and hinder incident response.

BVSS
Recommendation

A non-zero allowlist_admin value should be enforced, or an explicit “clear admin” workflow should be implemented that results in the emission of a dedicated event, ensuring the change is intentional and observable.

Remediation Comment

ACKNOWLEDGED: The Chainlink team acknowledged this finding and indicated that assigning the allowlist admin to the zero address should be allowed.

7.7 Fee withdrawal occurs prior to router/allowlist authorization

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Informational

Description

In ccip_send, the fee is withdrawn and deposited before checks for destination existence, allowlist membership, and router authorization are performed. Loss of funds on abort is prevented by Move's atomicity guarantees; however, gas usage for failing attempts is increased, and callers' griefing costs may be slightly amplified.

BVSS
Recommendation

Validation steps should be reordered so that low-cost checks are performed first; the fee should then be withdrawn, and token handling should be executed afterward.

Remediation Comment

ACKNOWLEDGED: The Chainlink team acknowledged this finding.

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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DestChainConfigV2 to Onramp- PR 287

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