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Fuelet Wallet Chrome Extension - Fuelet

Prepared by:

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HALBORN

Last Updated 12/19/2024

Date of Engagement: September 12th, 2024 - September 25th, 2024

Summary

100% of all REPORTED Findings have been addressed

All findings

3

Critical

0

High

1

Medium

2

Low

0

Informational

0

Table of Contents

1. Introduction

Fuelet engaged Halborn to conduct a security assessment of their Fuelet wallet Chrome extension, which began on September 12th, 2024 and ended on September 25th, 2024. The security assessment was scoped to the Fuelet wallet Chrome extension. The client team provided the source code to allow the security engineers to conduct testing using tools for scanning, detecting, and validating possible vulnerabilities, and report the findings at the end of the engagement.

2. Assessment Summary

The team at Halborn was provided a timeline for the engagement and assigned two full-time security engineers to verify the security of the assets in scope. The security engineers are penetration testing experts with advanced knowledge in web, mobile (Android and iOS), reconnaissance, blockchain and infrastructure penetration testing.

The goals of our security assessments are to improve the quality of the systems we review and to target sufficient remediation to help protect users.

During the security assessment, several vulnerabilities were identified that, while not critical, warrant attention to strengthen the application's overall security. Multiple valid account credentials were discovered in memory, highlighting an opportunity to enhance session management and secure storage practices. While the immediate risk of exploitation is limited, addressing this issue proactively will reduce the likelihood of unauthorized access or credential exposure. Additionally, the browser wallet does not lock upon instance closure, which, though not immediately critical, could lead to potential risks if user sessions are left unattended. Implementing proper wallet session isolation would improve user trust and mitigate potential security concerns.

Another observed issue was the persistence of sensitive information, such as passwords or keys, in the clipboard without automatic clearing mechanisms. Although this does not present an immediate threat, it may expose such data to interception if the system is compromised. Addressing these findings through secure coding practices and better session and memory management will help to mitigate risks while improving the application's security resilience over time.

For public release, this report was redacted per Fuelet request to exclude certain critical issues. It should be noted that all removed critical issues were fully addressed and resolved by the Fuelet team prior to the report's publication.

3. Test Approach and Methodology

Halborn followed a whitebox approach as per the scope and performed a combination of both manual and automated security testing to balance efficiency, timeliness, practicality, and accuracy regarding the scope of the pentest. While manual testing is recommended to uncover flaws in logic, process and implementation; automated testing techniques assist enhance coverage of the infrastructure and can quickly identify flaws in it.

The assessment methodology covered a range of phases of tests, and employed various tools, including but not limited to the following:

    • Verify minimum necessary permissions

    • Source code review

    • Hardcoded credentials or API keys

    • Sensitive data leakage

    • Robust Content Security Policy (CSP)

    • Manifest file configuration review

    • Validate and sanitize user inputs

    • Ensure sensitive data secure storage

    • Secure communications for all network communication

    • Security headers configuration

    • Ensure the least privileges for scripts

    • Component isolation verification

    • Third-party libraries review

    • Monitor extension behavior

    • Event listeners and handlers review

    • Data collection practices verification

    • Multiple browsers verification

    • Regulatory compliance

    • Static code analysis

    • Dynamic analysis

    • Review documentation completeness

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 (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}

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

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

6. Assessment Summary & Findings Overview

Critical

0

High

1

Medium

2

Low

0

Informational

0

Security analysisRisk levelRemediation Date
Multiple Valid Accounts Found in MemoryHighSolved - 10/15/2024
Wallet Not Locked on Browser Instance ClosingMediumSolved - 10/15/2024
Sensitive Information Available in the ClipboardMediumRisk Accepted - 10/15/2024

7. Findings & Tech Details

7.1 Multiple Valid Accounts Found in Memory

//

High

Description

In secure systems, private keys should only be available in memory for the shortest time necessary to perform cryptographic operations. If private keys are kept in memory for too long or are not properly cleared after use, they can be accessed by malicious actors through memory dumps, browser vulnerabilities, or malicious extensions. This poses a serious risk as an attacker can extract private keys from memory and use them to gain unauthorized access to accounts, sign transactions, or perform other critical actions on behalf of the user.

It was possible to retrieve the private key from the browser extension’s memory using basic memory inspection tools. If exploited, this could result in an attacker gaining unauthorized control of the user's accounts or assets.

Proof of Concept
Multiple hardcoded accounts in memoryValid account found with available funds
Score
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H(8.1)
Recommendation

  • Limit the Time Keys Stay in Memory: Private keys should only be loaded into memory during the specific cryptographic operation (e.g., signing a transaction) and immediately wiped from memory afterward. This reduces the window of opportunity for an attacker to access the key.

  • Use Secure Storage for Private Keys: Private keys should be stored securely (e.g., encrypted storage) and only decrypted into memory when absolutely necessary. After the operation, securely overwrite the memory to prevent the private key from remaining accessible.

  • Use WebCrypto API: When working with cryptographic operations in a browser environment, use the WebCrypto API. This API is designed to perform cryptographic operations in a way that prevents sensitive data, like private keys, from being exposed in the browser’s memory.

Remediation

SOLVED: The wallet extension showed valid private keys in memory, even after finish the browser session.

Example private key in memory

However, after a discussion with the internal team, we agreed that the private keys present in memory were regarding that the private keys and the assetID contains the same formats. No private keys from the imported or generated accounts were found in memory.

7.2 Wallet Not Locked on Browser Instance Closing

//

Medium

Description

The application is vulnerable due to the wallet remaining unlocked when the browser instance is closed. This security flaw occurs when a user’s wallet session persists even after the browser window or tab is closed, allowing the wallet to remain accessible without re-authentication upon reopening. This creates a critical security risk as it allows unauthorized access to the wallet, particularly in shared or public environments, or if the device is lost or compromised. This vulnerability undermines the security model that should protect sensitive user assets and private keys.

Proof of Concept

Execute an instance of the browser, open the wallet, close the browser instance and re-open to check that the wallet would remain unlocked

Score
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N(4.7)
Recommendation

Implement session management that automatically locks the wallet when the browser window or tab is closed. Require re-authentication (e.g., password, biometrics) when the user attempts to access the wallet again after a browser restart. Additionally, provide configurable timeout settings that automatically lock the wallet after a period of inactivity to further protect user assets. These measures will significantly enhance the security of the wallet and protect users against unauthorized access.

Remediation

SOLVED: The wallet extension locked correctly the wallet after session termination.

7.3 Sensitive Information Available in the Clipboard

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Medium

Description

The application allowed sensitive information, such as passwords, private keys, seed phrases, or personal data, to be copied to the clipboard without proper safeguards. When sensitive data is copied to the clipboard, it can be accessed by any other application running on the device, including malicious apps, keyloggers, or clipboard scrapers. This exposure creates a significant security risk, as clipboard data can be easily stolen or manipulated, leading to unauthorized access, data breaches, or identity theft.

The presence of sensitive information in the clipboard can lead to serious security consequences, including credential theft, account compromise, and financial loss. Attackers can monitor the clipboard to intercept copied data, allowing them to gain access to user accounts, wallets, or other protected resources. This vulnerability is particularly dangerous in shared or public devices, where clipboard data can persist beyond the intended session, inadvertently exposing private information to subsequent users or applications.

Proof of Concept
Private Key accessed by a third party applicationPrivate Key with copy functionality
Score
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:N/A:N(4.2)
Recommendation

Avoid copying sensitive information to the clipboard by default. Implement warnings or confirmation prompts when copying sensitive data is necessary, and consider automatically clearing the clipboard after a short interval or once the data is used.

Offer to the user the option to download the private key instead of using the clipboard functionality that can be accessed by a malicious crafted web application or third-party applications like terminal.

Remediation

RISK ACCEPTED: The Fuelet team accepted the risk of 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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