Mobile App Penetration Testing: Protection Against Malicious Apps

Imagine a typical scenario: a user opens a banking application, enters their username and password, and sees what appears to be a normal verification screen. But just seconds earlier, a malicious app installed from an unofficial source displayed a fake window over the legitimate interface. Any credentials entered during the attack were collected by the attacker. Neither the user nor the application owner noticed anything unusual.

This is how modern malicious mobile apps typically operate. They rarely attack directly. Instead, they look for vulnerabilities in legitimate applications, such as insecure data transmission, weak authentication, a lack of protection against reverse engineering, or excessive permissions.

By conducting mobile application penetration testing, organizations can identify these weaknesses before they are discovered by attackers. In this article, we explain how malicious mobile apps compromise legitimate applications, which vulnerabilities they exploit, and why regular mobile application penetration testing is not an expense but a necessity.

Malicious mobile apps and how they work

Malicious mobile apps are applications for mobile devices that perform hidden or harmful actions without the user's knowledge. In most cases, their malicious activity involves stealing data, tracking user activity, or disrupting the operation of other applications. Their defining characteristic is that they disguise themselves as legitimate or useful tools.

Main types of malicious mobile apps

Common distribution methods of malicious mobile apps

• APK files from third-party sources. These bypass the security checks performed by official app stores.
• Phishing links. They trick users into downloading fake applications that imitate well-known brands.
• Fake applications in official app stores. These disguise themselves as legitimate services and pass basic moderation checks.
• Social engineering. Attackers persuade users to grant excessive permissions or install malicious software.
• Malvertising. A single click on a malicious advertisement can result in malware being distributed through an advertising network.
• Compromised official app stores. Malicious code is embedded into applications that have already passed the store's review process.
• Malicious code embedded in third-party SDKs. It is integrated into libraries used by legitimate applications.

The impact of malicious mobile apps on application owners

Mobile application owners often underestimate this risk, but they should not. Their product can become not only the target of a cyberattack but also a tool used to attack its own users. We have seen this pattern time and again while working with companies across industries, including fintech and retail.

This typically leads to the following consequences:

• Theft of user data. This can expose the application owner to significant legal liability if the breach was made possible by a vulnerability in the application.
• Reputational damage. Even a single publicly disclosed security incident can lower an application's rating, generate negative reviews, and require months to rebuild user trust.
• Financial losses. Compensation for affected users, incident response costs, and lost revenue during service disruptions often exceed the cost of preventive mobile application penetration testing.
• Legal and regulatory consequences. Violations of GDPR or other personal data protection regulations can result in regulatory investigations and substantial fines, with long-term business consequences.

How malicious mobile apps exploit legitimate applications

Let's examine the most common techniques malicious mobile applications use to compromise legitimate apps.

1. Credential theft

What happens: A malicious application intercepts authentication credentials as they are entered, including usernames, passwords, and banking information.

What it looks like to the user: The application appears to freeze or unexpectedly asks the user to enter their credentials again.

Business impact: Large-scale compromise of customer accounts, financial losses, and violations of data protection regulations.

2. Overlay attacks

What happens: A fake interface is displayed over the legitimate application screen.

What it looks like to the user: The interface appears completely normal, with no visible signs of suspicious activity.

Business impact: Mass compromise of user accounts and serious reputational damage to the application's brand.

3. Man-in-the-Middle (MitM) attacks

What happens: An attacker intercepts traffic between the application and the server due to missing certificate validation or the absence of SSL pinning.

What it looks like to the user: The application continues to function normally without any visible warning signs.

Business impact: Real-time exposure of authorization tokens, personal information, and financial data.

4. Reverse engineering of mobile applications

What happens: An attacker decompiles the application's APK file, analyzes the source code, and discovers encryption keys, API tokens, and business logic.

What it looks like to the user: The attack takes place outside the device, so the user notices nothing unusual.

Business impact: Compromise of backend systems, exposure of confidential business information, and the ability to create a fake version of the application.

5. Abuse of permissions and accessibility service

What happens: A malicious application requests excessive permissions or abuses Android's Accessibility Service to gain control over other applications.

What it looks like to the user: The application simply requests standard permissions during installation, with no obvious signs of malicious behavior.

Business impact: Unauthorized data collection, violations of user privacy, and potential legal liability.

How to protect a legitimate mobile application from malicious mobile apps

Below are the key security measures we recommend implementing in mobile applications. Each of these is intended to defend against the attack methods described above.

Mobile application pentest as a cybersecurity assessment method

To begin with, it is important to understand what penetration testing is. It is a structured security assessment that imitates real-world attack methods. Cybersecurity specialists reproduce the actions of an attacker by attempting to steal data, bypass authentication, decompile code, perform overlay attacks, and document everything that can be successfully exploited. Its purpose is to identify vulnerabilities before they are discovered by malicious actors.

Based on the extensive experience of our specialists, most vulnerabilities discovered during penetration testing are not the result of highly sophisticated attacks. They are typically common technical weaknesses, such as insecure data transmission, missing SSL pinning, or sensitive information stored in plaintext on the device. These issues can only be identified through targeted security testing.

For example, during the penetration test of an iOS application for an insurance company, the Datami team identified critical vulnerabilities that could potentially allow attackers to intercept authentication data - issues that would likely have remained undetected during standard functional testing. In another mobile application penetration testing case involving reverse engineering, we were able to gain access to critical backend components through insufficiently protected compiled code.

Main stages of mobile application penetration testing

A typical penetration testing process consists of 7 stages:

1. Information gathering. At this stage, the scope of the assessment is defined, publicly available and technical information about the target system is collected, and all findings are documented.
2. Reconnaissance. Security experts gather information through passive and active techniques to gain a detailed understanding of the target environment.
3. Discovery and scanning. Penetration testers identify active hosts, open ports, running services, and potential vulnerabilities.
4. Vulnerability assessment. The collected data is analyzed, the risk level of each vulnerability is determined, and remediation priorities are established.
5. Exploitation. Identified vulnerabilities are safely exploited in a controlled environment to verify attack feasibility and assess their real-world impact.
6. Final analysis and reporting. Following the assessment, a report is prepared that details the discovered vulnerabilities, evaluates their potential impact, and provides remediation recommendations.
7. Implementation of findings. The organization applies the recommendations, updates security policies, trains personnel, and establishes ongoing security monitoring.

When should mobile app pentesting be performed

We recommend conducting penetration testing in the following situations:

• During development. To build the application's architecture with security as a core consideration from the start.
• Before release. To avoid launching an application with known vulnerabilities.
• After major updates. New functionality may expose the application to additional security risks.
• After integrating third-party SDKs or libraries. External components may contain vulnerabilities of their own.
• After detecting suspicious activity. To assess the scope and nature of a potential security compromise.
• As a regular part of maintenance. Effective security depends on continuous evaluation rather than a one-time review.

Vulnerabilities identified through mobile application penetration testing

Cybersecurity includes many different types of cybersecurity vulnerabilities that can affect systems and applications. Below are the ones most commonly identified during mobile application penetration testing and most frequently exploited by malicious mobile apps.

Conclusion

Malicious mobile apps represent a real and growing threat not only to end users but also to mobile application owners. They exploit vulnerabilities in application code, insecure communications, excessive permissions, and the absence of protection against reverse engineering.

Mobile application penetration testing allows you to evaluate your product from an attacker's perspective by identifying weaknesses, assessing its actual security posture, and providing clear recommendations for remediation. Based on our experience, regular mobile application penetration testing is an investment in the long-term resilience of your product and the trust of your users.

If your mobile application has never undergone a penetration test, or if you want to assess its current level of security, request a consultation with Datami's specialists. We perform penetration testing for iOS and Android applications and provide a detailed report describing identified vulnerabilities along with practical recommendations for remediation.

Glossary of terms

A glossary of the key terms used in this article: