Introduction
We express our gratitude to the Blubird team for the collaborative engagement that enabled the execution of this Smart Contract Security Assessment.
Blubird consists of an ERC20 token featuring configurable minting, burning, and pausing capabilities, alongside a token distribution contract that manages allocations with flexible vesting schedules, supply caps, and time-based claims.
Document | |
|---|---|
| Name | Smart Contract Code Review and Security Analysis Report for Blubird |
| Audited By | Kornel Światłowski, David Camps |
| Approved By | Ivan Bondar |
| Website | https://www.getblubird.com/→ |
| Changelog | 28/07/2025 - Preliminary Report |
| 01/08/2025 - Final Report | |
| 12/08/2025 - Updated Final Report | |
| Platform | ETH/EVM |
| Language | Solidity |
| Tags | Claims, ERC-20, Timelock, Vesting. |
| Methodology | https://hackenio.cc/sc_methodology→ |
Document
- Name
- Smart Contract Code Review and Security Analysis Report for Blubird
- Audited By
- Kornel Światłowski, David Camps
- Approved By
- Ivan Bondar
- Website
- https://www.getblubird.com/→
- Changelog
- 28/07/2025 - Preliminary Report
- 01/08/2025 - Final Report
- 12/08/2025 - Updated Final Report
- Platform
- ETH/EVM
- Language
- Solidity
- Tags
- Claims, ERC-20, Timelock, Vesting.
- Methodology
- https://hackenio.cc/sc_methodology→
Review Scope | |
|---|---|
| Repository | https://github.com/BluBird-App/BluBirdAdmin-Backend→ |
| Commit | f09c89c |
| Remediation Commit | 0c1ba84 |
| Updated Remediation Commit | 459954d |
Review Scope
- Commit
- f09c89c
- Remediation Commit
- 0c1ba84
- Updated Remediation Commit
- 459954d
Audit Summary
The system users should acknowledge all the risks summed up in the risks section of the report
Documentation quality
Functional requirements are present, but only at a high-level.
Overall system requirements are provided.
Basic system description is provided.
No roles description.
No NatSpec.
Technical description was not provided.
Code quality
The development environment is configured.
Test coverage
Code coverage of the project is 98.68% (branch coverage).
Deployment and basic user interactions are covered with tests.
Negative cases coverage is present.
System Overview
ERC20Token - The contract implements a configurable ERC20 token with optional minting, burning, and pausing features. Functionality is based on OpenZeppelin extensions, with feature flags controlling access to minting and burning logic as well as pause mechanisms. A custom decimal precision is defined at deployment, and initial supply can be optionally minted to the deployer.
ILDistribution - The contract implements a token distribution system with configurable allocation types, supporting linear and periodic vesting schedules, optional lockup periods, and optional immediate release. Allocation types define supply caps and are assigned to recipients with per-allocation tracking for claimed and unclaimed amounts. Token claims are based on time-based release logic, and optional cancellation or instant release can be toggled at deployment. Administrative functions allow batch processing of allocations
Privileged roles
The ERC20Token contract uses an Ownable mechanism from OpenZeppelin for access control. The contract owner can call:
mint()– mints tokens to a specified address if minting is enabledpause()– pauses all token transfers if the pausing feature is enabledunpause()– resumes token transfers if the pausing feature is enabled
The ILDistribution contract uses an AccessControl mechanism from OpenZeppelin for access control. The DEFAULT_ADMIN_ROLE can call:
setToken()– sets the token used for distributionaddAllocation()– adds a single allocation to a recipientaddAllocations()– adds multiple allocations in a batchraiseAllocation()– increases the amount of a specific allocationraiseAllocations()– increases the amount for multiple allocationscancelAllocation()– cancels an individual allocationcancelAllocations()– cancels multiple allocations in a batchrefundTokens()– transfers out specified ERC20 tokens from the contract
Potential Risks
Centralized Control of Minting Process: The token contract’s design allows for centralized control over the minting process, posing a risk of unauthorized token issuance, potentially diluting the token value and undermining trust in the project's economic governance.
Centralized Minting to a Single Address: The project concentrates minting tokens in a single address, raising the risk of fund mismanagement or theft, especially if key storage security is compromised.
Single Points of Failure and Control: The project is fully or partially centralized, introducing single points of failure and control. This centralization can lead to vulnerabilities in decision-making and operational processes, making the system more susceptible to targeted attacks or manipulation.
Administrative Key Control Risks: The digital contract architecture relies on administrative keys for critical operations. Centralized control over these keys presents a significant security risk, as compromise or misuse can lead to unauthorized actions or loss of funds.
The ERC20 token contract does not enforce a maximum supply cap, allowing unlimited minting. This introduces a monetary policy risk, as unchecked inflation can dilute existing holders, reduce trust in the token’s value, and lead to potential abuse by privileged roles. Without a hard cap or clearly defined minting rules, the token’s economic model lacks predictability, which may deter users and integrations with external protocols.
The ERC20 token contract includes a pausability mechanism that allows privileged roles to halt transfers at any time. While useful for emergency control, this introduces centralization risk, as token holders are exposed to arbitrary disruption of transfers, which may affect usability, investor confidence, and integration with third-party protocols that rely on uninterrupted token functionality.
The ERC20 token contract allows users to burn their own tokens and permits third parties to burn tokens on behalf of others if granted allowance. While this functionality can be intentional and useful (e.g., for deflationary models), it introduces a token supply reduction mechanism that, if misused or poorly understood, could lead to unexpected token loss. Projects should clearly document this behavior and ensure interfaces or integrations handle it safely to avoid accidental or unintended burns.
The contract does not include a direct mechanism to recover tokens that may become unintentionally stuck in vesting allocations. While this could temporarily restrict access to those tokens, the impact is mitigated by the ability to create new vesting allocations to withdraw and redistribute the locked tokens.
The claim and claimAll functions lack explicit access control, allowing any user to invoke them. While this does not pose a severe risk—since tokens can only be claimed from existing allocations and ultimately benefit the allocation owner—this unrestricted access may lead to unintended interactions.
Findings
Code ― | Title | Status | Severity | |
|---|---|---|---|---|
| F-2025-1212 | Incorrect Percentage Returned Before Token Release Start | fixed | Low | |
| F-2025-1193 | Release Schedule Start Time Can Be Set in the Past | accepted | Observation | |
| F-2025-1192 | Revert Error Messages are Split Across Multiple Strings | fixed | Observation | |
| F-2025-1192 | Inefficient Array Length Access in claimable() and claimAll() | fixed | Observation | |
| F-2025-1190 | Commented Code Parts | fixed | Observation | |
| F-2025-1189 | Redundant Variable Initialization Increases Deployment Gas Cost | fixed | Observation | |
| F-2025-1189 | Floating Pragma | fixed | Observation |
Appendix 1. Definitions
Severities
When auditing smart contracts, Hacken is using a risk-based approach that considers Likelihood, Impact, Exploitability and Complexity metrics to evaluate findings and score severities.
Reference on how risk scoring is done is available through the repository in our Github organization:
Severity | Description |
|---|---|
Critical | Critical vulnerabilities are usually straightforward to exploit and can lead to the loss of user funds or contract state manipulation. |
High | High vulnerabilities are usually harder to exploit, requiring specific conditions, or have a more limited scope, but can still lead to the loss of user funds or contract state manipulation. |
Medium | Medium vulnerabilities are usually limited to state manipulations and, in most cases, cannot lead to asset loss. Contradictions and requirements violations. Major deviations from best practices are also in this category. |
Low | Major deviations from best practices or major Gas inefficiency. These issues will not have a significant impact on code execution. |
Severity
- Critical
Description
- Critical vulnerabilities are usually straightforward to exploit and can lead to the loss of user funds or contract state manipulation.
Severity
- High
Description
- High vulnerabilities are usually harder to exploit, requiring specific conditions, or have a more limited scope, but can still lead to the loss of user funds or contract state manipulation.
Severity
- Medium
Description
- Medium vulnerabilities are usually limited to state manipulations and, in most cases, cannot lead to asset loss. Contradictions and requirements violations. Major deviations from best practices are also in this category.
Severity
- Low
Description
- Major deviations from best practices or major Gas inefficiency. These issues will not have a significant impact on code execution.
Potential Risks
The "Potential Risks" section identifies issues that are not direct security vulnerabilities but could still affect the project’s performance, reliability, or user trust. These risks arise from design choices, architectural decisions, or operational practices that, while not immediately exploitable, may lead to problems under certain conditions. Additionally, potential risks can impact the quality of the audit itself, as they may involve external factors or components beyond the scope of the audit, leading to incomplete assessments or oversight of key areas. This section aims to provide a broader perspective on factors that could affect the project's long-term security, functionality, and the comprehensiveness of the audit findings.
Appendix 2. Scope
The scope of the project includes the following smart contracts from the provided repository:
Scope Details | |
|---|---|
| Repository | https://github.com/BluBird-App/BluBirdAdmin-Backend→ |
| Commit | f09c89c |
| FinalCommit | 0c1ba84 |
| Updated Remediation Commit | 459954d |
| Whitepaper | N/A |
| Requirements | https://docs.google.com/document/d/1hweed4rZqc4I2IyHRUuTcStZIJeAwiPZ3uCLEaqEiug/edit?usp=sharing;→ |
| Technical Requirements | https://docs.google.com/document/d/1hweed4rZqc4I2IyHRUuTcStZIJeAwiPZ3uCLEaqEiug/edit?usp=sharing;→ |
Scope Details
- Commit
- f09c89c
- FinalCommit
- 0c1ba84
- Updated Remediation Commit
- 459954d
- Whitepaper
- N/A
Assets in Scope
Appendix 3. Additional Valuables
Verification of System Invariants
During the audit of Blubird / BluBirdAdmin-Backend, Hacken followed its methodology by performing fuzz-testing on the project's main functions. Foundry →, a tool used for fuzz-testing, was employed to check how the protocol behaves under various inputs. Due to the complex and dynamic interactions within the protocol, unexpected edge cases might arise. Therefore, it was important to use fuzz-testing to ensure that several system invariants hold true in all situations.
Fuzz-testing allows the input of many random data points into the system, helping to identify issues that regular testing might miss. A specific Foundry fuzzing suite was prepared for this task, and throughout the assessment, 7 invariants were tested over 10000 runs each. This thorough testing ensured that the system works correctly even with unexpected or unusual inputs.
Invariant | Test Result | Run Count |
|---|---|---|
| Total supply equals sum of contract and user balances | Passed | 10000 |
| Allocated amounts never exceed allocation type supply | Passed | 10000 |
| Total claimed tokens match actual tokens transferred from contract | Passed | 10000 |
| Total claimed tokens equal sum of all user balances | Passed | 10000 |
| Each user's token balance equals their total claimed tokens | Passed | 10000 |
| Total claimable tokens do not exceed contract token balance | Passed | 10000 |
| Number of canceled allocations never exceeds number of created allocations | Passed | 10000 |
Invariant
- Total supply equals sum of contract and user balances
Test Result
- Passed
Run Count
- 10000
Invariant
- Allocated amounts never exceed allocation type supply
Test Result
- Passed
Run Count
- 10000
Invariant
- Total claimed tokens match actual tokens transferred from contract
Test Result
- Passed
Run Count
- 10000
Invariant
- Total claimed tokens equal sum of all user balances
Test Result
- Passed
Run Count
- 10000
Invariant
- Each user's token balance equals their total claimed tokens
Test Result
- Passed
Run Count
- 10000
Invariant
- Total claimable tokens do not exceed contract token balance
Test Result
- Passed
Run Count
- 10000
Invariant
- Number of canceled allocations never exceeds number of created allocations
Test Result
- Passed
Run Count
- 10000
Additional Recommendations
The smart contracts in the scope of this audit could benefit from the introduction of automatic emergency actions for critical activities, such as unauthorized operations like ownership changes or proxy upgrades, as well as unexpected fund manipulations, including large withdrawals or minting events. Adding such mechanisms would enable the protocol to react automatically to unusual activity, ensuring that the contract remains secure and functions as intended.
To improve functionality, these emergency actions could be designed to trigger under specific conditions, such as:
Detecting changes to ownership or critical permissions.
Monitoring large or unexpected transactions and minting events.
Pausing operations when irregularities are identified.
These enhancements would provide an added layer of security, making the contract more robust and better equipped to handle unexpected situations while maintaining smooth operations.