OWASP Top 10 for Mobile Apps: M7 – Client Code Quality

OWASP Top 10 for Mobile Apps: M7 – Client Code Quality

Introduction

The OWASP (Open Web Application Security Project) Top 10 for Mobile Apps serves as a crucial guide for securing mobile applications. Among its categories, M7: Client Code Quality is often overlooked despite being fundamental to the robustness and security of any mobile app. For software developers and penetration testers, understanding and addressing client code quality issues is essential not just for the app’s performance but also for its ability to withstand malicious exploitation.

This article delves deep into M7, providing an exhaustive exploration tailored for professionals, with actionable insights to improve mobile application security.

What is M7: Client Code Quality?

Client code quality refers to the soundness, reliability, and maintainability of the code executed on mobile devices. The “M7” designation in the OWASP Top 10 highlights vulnerabilities resulting from poorly written client-side code. These vulnerabilities can stem from inadequate input validation, insecure coding practices, or the use of deprecated libraries.

Flawed client code exposes apps to a range of attacks, such as:

• Data exfiltration
• Code tampering
• Debugging exploits
• Reverse engineering for intellectual property theft

For developers and testers, ensuring robust client code quality isn’t just a technical necessity—it’s a critical component of safeguarding user trust and minimising reputational risks for businesses.

The Business Impact of Poor Client Code Quality

1. Financial Losses

Organisations with compromised apps often face significant financial repercussions, from legal penalties to customer reimbursements. Breaches arising from M7 issues may allow attackers to exploit apps for fraud or monetise stolen intellectual property.

2. Loss of Consumer Trust

Applications riddled with security flaws erode customer confidence. Once users lose trust, they are less likely to engage with the product or recommend it, diminishing both direct revenue and long-term brand loyalty.

3. Regulatory Compliance Challenges

In many jurisdictions, apps handling sensitive user data must comply with regulations such as GDPR or CCPA. Poor client code practices that lead to data breaches can attract severe penalties and class-action lawsuits.

Common Vulnerabilities in Client Code Quality

Understanding frequent issues allows professionals to identify and mitigate vulnerabilities early. Below are some common vulnerabilities related to M7:

1. Lack of Input Validation

Improper input validation is a gateway for malicious actors. Examples include buffer overflow attacks or injection vulnerabilities, where attackers send unexpected input to crash or manipulate the app.

Example:

A shopping app failing to validate quantity inputs may allow attackers to bypass limits by entering negative numbers, leading to free product allocations or inventory mismanagement.

2. Use of Insecure Libraries

Incorporating third-party libraries without thorough vetting can introduce significant vulnerabilities. Outdated or poorly maintained libraries often contain exploitable flaws.

Case Study:

The 2019 WhatsApp vulnerability that allowed attackers to inject spyware via video calls stemmed from an issue in a third-party library.

3. Code Tampering Risks

Static and dynamic analysis tools, when poorly implemented, make it easy for attackers to reverse engineer or tamper with apps, often leading to data theft or piracy.

Example:

An app lacking obfuscation or encryption may allow an attacker to retrieve API keys or manipulate functionality.

4. Insufficient Error Handling

Exposing stack traces or error messages can reveal sensitive information about the app’s logic or infrastructure.

Strategies for Improving Client Code Quality

1. Adopting Secure Coding Practices

Follow guidelines such as OWASP’s Secure Coding Principles to ensure consistent and safe coding practices. For instance:

• Validate inputs rigorously.
• Encrypt sensitive data both in transit and at rest.
• Implement strong authentication mechanisms.

2. Static and Dynamic Code Analysis

Employ static code analysis tools like SonarQube to catch vulnerabilities at compile time. Complement this with dynamic tools that simulate runtime environments for identifying performance and security issues.

3. Leveraging Obfuscation

Code obfuscation increases the difficulty of reverse engineering. While not a complete solution, it adds a crucial layer of protection against tampering.

Tip: Use tools like ProGuard for Android or SwiftShield for iOS to obfuscate code effectively.

4. Monitoring Third-Party Libraries

Regularly audit and update third-party dependencies. Tools like Dependabot or Snyk help track vulnerabilities in external libraries and recommend patches.

The Role of Penetration Testing in M7

1. Identifying Vulnerabilities Proactively

Penetration testing mimics real-world attack scenarios to assess the app’s resilience against exploitation. Testers should focus on areas like encryption flaws, unsecured APIs, and tampering opportunities.

2. Enhancing Feedback Loops

Penetration tests uncover actionable insights for development teams. By embedding security testers into agile workflows, organisations can implement timely improvements.

Tools and Techniques for Developers and Testers

Static Analysis Tools

• Checkmarx: Comprehensive SAST tool for identifying coding errors.
• Fortify Static Code Analyzer: Industry leader in pinpointing client-side vulnerabilities.

Dynamic Analysis Tools

• Burp Suite: Excellent for simulating live attacks on APIs and interfaces.
• ZAP (Zed Attack Proxy): Open-source tool ideal for penetration testers assessing real-time app behaviours.

Obfuscation Tools

• DexGuard: Advanced obfuscation for Android apps.
• iXGuard: Tailored for iOS platforms.

Case Study: Poor Client Code Quality in Action

Background:

In 2020, a widely used healthcare app was compromised, exposing sensitive patient data. Attackers exploited unvalidated input fields to escalate privileges within the system.

Outcome:

The breach resulted in a £2 million fine under GDPR, along with a significant drop in user retention rates.

Lesson Learned:

Secure client-side coding and regular penetration testing would have detected this issue before deployment.

Cyber Incidents Attributable to M7: Client Code Quality

Poor client code quality has historically been a root cause of significant cyber incidents. By exploring real-world examples, we can better understand the potential consequences of M7 vulnerabilities and the lessons they impart.

1. WhatsApp Pegasus Exploit (2019)

Incident Overview

The infamous Pegasus spyware, developed by NSO Group, exploited a vulnerability in WhatsApp’s client code. Attackers used a buffer overflow vulnerability in the app’s voice call feature to inject malicious code into target devices. This allowed them to install spyware, gaining full access to device data, including messages, emails, and cameras.

Connection to M7

• The vulnerability was rooted in inadequate input validation within WhatsApp’s client-side library for handling VoIP calls.
• The flawed client code allowed attackers to craft a specially designed packet that triggered unauthorised execution of malicious code.

Impact

• Over 1,400 users, including journalists and human rights activists, were targeted globally.
• Facebook (WhatsApp’s parent company) faced lawsuits and severe reputational damage.

Lesson Learned

• Implementing rigorous input validation and dynamic analysis during development could have mitigated this vulnerability.
• Regular patching and third-party library audits are critical for addressing client-side code risks.

2. Starbucks Mobile App Vulnerability (2014)

Incident Overview

Starbucks’ mobile app, one of the most widely used coffee shop apps, stored user credentials (usernames and passwords) in plain text on mobile devices. Anyone with physical access to the phone could retrieve this sensitive information.

Connection to M7

• The incident highlighted poor data handling practices in client code. Sensitive information was neither encrypted nor protected through secure storage mechanisms.
• Lack of proper code review and testing contributed to the issue.

Impact

• The vulnerability exposed millions of users’ sensitive credentials, creating trust issues for Starbucks’ digital platform.
• Though no significant breaches were reported, the incident served as a cautionary tale.

Lesson Learned

• Sensitive data in client-side code should always be encrypted, and secure storage APIs must be employed.
• Developers should avoid hardcoding sensitive credentials into apps.

3. Grindr Data Exposure (2018)

Incident Overview

Grindr, a popular dating app, faced scrutiny when researchers discovered it was leaking sensitive user data, including location and private preferences, to third-party ad networks. This was due to insecure coding practices and improper handling of API responses.

Connection to M7

• Poor API integration and error handling in client-side code exposed user data to unauthorised parties.
• The client-side app failed to obfuscate critical endpoints, making it easier for attackers to analyse network traffic and exploit weaknesses.

Impact

• Grindr faced intense public backlash for compromising user privacy.
• Regulatory bodies began scrutinising data-sharing practices more closely.

Lesson Learned

• Employ secure coding techniques for APIs, including data minimisation and encryption.
• Integrating penetration testing into the development lifecycle could have revealed these vulnerabilities.

4. Uber Data Breach (2016)

Incident Overview

Uber suffered a significant data breach when attackers accessed its systems using stolen credentials embedded in the app. The root cause was exposed API keys hardcoded in the mobile app’s client code, enabling attackers to escalate privileges and compromise servers.

Connection to M7

• Hardcoding sensitive credentials directly within the client code was a critical M7 violation.
• Lack of obfuscation and secure storage practices increased the app’s attack surface.

Impact

• The breach exposed the personal data of 57 million customers and drivers.
• Uber paid $148 million in fines and faced immense reputational damage.

Lesson Learned

• Avoid embedding sensitive information in client-side code. Use secure vaults or server-side mechanisms for managing credentials.
• Obfuscation tools should be a standard practice for protecting critical sections of code.

5. Pokémon GO Vulnerability (2016)

Incident Overview

Shortly after Pokémon GO’s release, attackers discovered that the app requested excessive permissions on Android devices, including full access to users’ Google accounts. The client code’s poorly designed permission requests raised security alarms.

Connection to M7

• Over-permissioning in the client code was a glaring issue.
• Insufficient testing allowed excessive permissions to go unnoticed before deployment.

Impact

• The incident sparked privacy concerns among millions of users.
• Although the issue was resolved quickly, the reputation of the app’s developers, Niantic, took a temporary hit.

Lesson Learned

• Mobile apps should follow the principle of least privilege, requesting only the permissions necessary for functionality.
• Comprehensive client-side security testing during development can prevent such issues.

6. TikTok Vulnerabilities (2020)

Incident Overview

Researchers discovered multiple vulnerabilities in TikTok’s mobile app, including one that allowed attackers to manipulate HTTP requests to hijack user accounts. This was facilitated by weak client-side code that failed to validate request origins or implement secure communication channels.

Connection to M7

• Weak input validation and lack of integrity checks in the client code made the app vulnerable to request forgery attacks.
• Poor coding standards exposed users to account takeovers and data theft.

Impact

• TikTok faced global criticism and investigations into its data security practices.
• The vulnerabilities amplified concerns about the app’s broader security posture.

Lesson Learned

• Strong validation mechanisms must be built into client-side code to detect and block malicious requests.
• Secure transport layers (e.g., HTTPS with strict certificate validation) are essential for protecting communications.

M7 vulnerabilities have been exploited in various other high-profile cyber incidents, further showcasing how poor client code quality can lead to serious breaches. Below are additional examples illustrating the significance of addressing these issues.

7. Snapchat API Exploitation (2014)

Incident Overview

Snapchat suffered a major breach when attackers exploited a weakness in its client API, allowing them to harvest usernames and phone numbers of approximately 4.6 million users. The client code failed to properly validate requests, making it susceptible to brute force attacks.

Connection to M7

• The lack of rate-limiting and request validation in client code allowed attackers to enumerate phone numbers systematically.
• Snapchat’s weak error-handling mechanisms exposed it to exploitation.

Impact

• The incident eroded user trust in Snapchat’s security measures.
• It highlighted the platform’s negligence in implementing basic security best practices.

Lesson Learned

• Client-side code must include robust input validation and rate-limiting mechanisms.
• Regular API audits and penetration testing are critical to uncover such vulnerabilities before exploitation.

8. Strava Fitness Tracker Privacy Issue (2018)

Incident Overview

Strava, a fitness tracking app, inadvertently exposed sensitive military base locations through its public heatmap feature. The app’s client-side code allowed users’ GPS data to be uploaded and visualised without sufficient anonymisation.

Connection to M7

• Inadequate data anonymisation and failure to enforce secure data transmission highlighted poor client-side coding practices.
• The app’s client code did not offer users granular control over privacy settings.

Impact

• The exposure revealed the locations of secret military installations, putting national security at risk.
• Strava faced public backlash and scrutiny over its handling of user data.

Lesson Learned

• Privacy-by-design principles must be incorporated into client-side code.
• Data anonymisation and encryption should be integral to all mobile app development processes.

9. LINE Messaging App Vulnerability (2016)

Incident Overview

The LINE messaging app was found to store user chat logs in plaintext on devices, making them accessible to malware or attackers with physical access to the phone. The issue stemmed from insecure client-side data storage practices.

Connection to M7

• Poor data protection practices in the client code led to sensitive information being stored without encryption.
• Failure to use secure storage APIs exemplified weak client-side security measures.

Impact

• The incident damaged LINE’s reputation as a secure communication app.
• It raised awareness about the importance of encrypted local storage for sensitive data.

Lesson Learned

• Secure storage APIs and end-to-end encryption should be default practices in messaging apps.
• Developers must audit storage mechanisms to ensure compliance with security standards.

10. PayPal Mobile App Authentication Flaw (2013)

Incident Overview

A critical vulnerability in PayPal’s mobile app allowed attackers to bypass authentication and access user accounts. The issue stemmed from insecure authentication logic in the client code, which failed to validate user sessions effectively.

Connection to M7

• Weak session management and authentication logic in the client code created a pathway for attackers to hijack user accounts.
• Insufficient input validation and poor error handling amplified the problem.

Impact

• The vulnerability exposed sensitive user financial information.
• PayPal faced customer dissatisfaction and criticism for its inadequate security measures.

Lesson Learned

• Strong authentication mechanisms must be implemented in client-side code.
• Security testing for authentication workflows is vital to prevent such incidents.

11. EA Origin Account Takeover (2019)

Incident Overview

Attackers exploited vulnerabilities in EA’s Origin gaming platform to hijack user accounts. The issue originated from weak token validation and flawed redirect mechanisms in the mobile client’s code.

Connection to M7

• Insecure token management and redirect handling were clear indicators of poor client-side coding practices.
• The vulnerability allowed attackers to craft malicious links that stole user tokens.

Impact

• Thousands of gaming accounts were compromised.
• EA had to release emergency patches to fix the client-side flaws.

Lesson Learned

• Developers should use secure token management techniques and sanitise redirect URLs.
• Penetration testing focusing on session management can proactively identify such vulnerabilities.

12. Uber Hardcoded Secrets Revisited (2022)

Incident Overview

Uber faced another data breach when attackers discovered hardcoded API keys in their mobile app’s client code. This oversight allowed attackers to access sensitive backend systems and leak data.

Connection to M7

• Embedding sensitive information such as API keys and secrets in client-side code violates security best practices.
• Poor obfuscation practices made it easy for attackers to reverse-engineer the app and extract sensitive information.

Impact

• The breach highlighted Uber’s recurring failure to secure client-side code.
• The incident emphasised the risks of neglecting secure coding practices, even for established organisations.

Lesson Learned

• API keys and secrets should never be stored in client code.
• Obfuscation tools and server-side authentication mechanisms are essential safeguards.

13. Samsung SmartThings App Vulnerabilities (2016)

Incident Overview

The SmartThings app, used for managing IoT devices, contained vulnerabilities that allowed attackers to control smart home devices remotely. Weak client-side code failed to validate device permissions adequately.

Connection to M7

• Inadequate permission validation and poor security design in the client code allowed attackers to manipulate device configurations.
• The app’s weak error-handling mechanisms facilitated unauthorised access.

Impact

• The incident raised significant concerns about IoT security.
• Samsung had to issue urgent updates and invest in better app security protocols.

Lesson Learned

• Secure permission handling should be a priority in client-side IoT apps.
• IoT app developers must adopt secure coding standards and conduct thorough penetration testing.

14. Robinhood API Abuse (2021)

Incident Overview

Attackers exploited Robinhood’s API through flaws in its mobile app’s client code, allowing them to brute force account credentials and bypass 2FA mechanisms. The issue was rooted in the app’s failure to implement rate-limiting and CAPTCHA validation.

Connection to M7

• Poor input validation and lack of brute force protection in the client code made the app vulnerable.
• Weak session management practices further exposed users to account takeovers.

Impact

• The breach resulted in compromised accounts and financial losses for users.
• Robinhood faced regulatory scrutiny and reputational damage.

Lesson Learned

• Rate-limiting, CAPTCHA, and robust input validation must be integral to client-side code.
• Security measures should be regularly tested to ensure resilience against evolving threats.

15. WeChat Miscreants-in-the-Middle Attack (2015)

Incident Overview

Researchers discovered that WeChat’s client-side code failed to enforce strict SSL certificate validation, leaving the app susceptible to miscreants-in-the-middle (MITM) attacks. This allowed attackers to intercept sensitive communications.

Connection to M7

• The client code’s inadequate SSL validation represented a critical security flaw.
• Weak transport layer security exposed users to significant risks.

Impact

• The vulnerability raised questions about the app’s commitment to user security.
• Tencent, WeChat’s parent company, had to implement emergency fixes and rebuild user trust.

Lesson Learned

• Strict SSL validation and certificate pinning should be standard in client-side applications.
• Regular security testing must include network layer vulnerabilities.

By analysing these incidents, software developers and penetration testers can gain valuable insights into how poor client-side code quality (M7) can lead to severe consequences. Addressing these issues proactively ensures robust mobile app security, protecting users and businesses alike.

Practical Tips for Developers

1. Educate Your Team:
   
   Conduct regular training sessions on secure coding standards.
   
2. Automate Where Possible:
   
   Automate code reviews and testing workflows using CI/CD pipelines integrated with security tools.
   
3. Test Under Adverse Conditions:
   
   Simulate low-memory or high-load environments to test app resilience.
   
4. Prioritise Updates:
   
   Create a policy for frequent updates of third-party libraries and frameworks.
   

Final Thoughts

M7: Client Code Quality is not just a technical concern—it’s a business-critical issue. For developers, building secure and efficient mobile apps demands an unwavering commitment to high coding standards and continuous improvement. For penetration testers, providing actionable feedback ensures the robustness of mobile applications, protecting both users and enterprises.

In a world increasingly reliant on mobile solutions, addressing M7 vulnerabilities is indispensable for achieving a secure digital ecosystem. Prioritising client code quality will yield not only secure apps but also satisfied users and a resilient reputation for organisations.

By adhering to these principles and leveraging the strategies outlined above, developers and testers can transform the challenge of securing mobile apps into an opportunity for innovation and trust-building.

These incidents underline the critical importance of addressing M7 vulnerabilities in mobile applications. Poor client code quality doesn’t just compromise technical integrity—it has real-world consequences, including financial losses, reputational harm, and legal penalties. Developers and penetration testers must prioritise secure coding practices, rigorous testing, and proactive risk management to mitigate such risks effectively. By learning from past incidents, organisations can fortify their apps and build user trust in an increasingly interconnected world.