When organizations consider securing their mobile applications, the focus often remains server-side APIs. Ideally, this makes a lot of sense since APIs are a common attack surface, and in many cases, the same APIs are leveraged by both web and mobile applications. Security teams usually include these APIs thoroughly as part of web application assessments and penetration testing.
Another critical dimension when it comes to a mobile app architecture is the mobile client itself. A mobile application running on user devices introduce various risks, particularly around data storage & leakage - what data gets stored locally and how that data can be accessed. If we look at the three most common scenarios that make this critical: -
1. Data Stored on the Client Side (On Mobile Device)
One of the most critical risks that organizations face unknowingly is what data is being stored on the device. If sensitive information such as authentication tokens, personal/PII data, or files with confidential information are cached insecurely, attackers with device access could exploit it.
2. Company-Owned Devices with Third-Party Apps
In some environments, companies use MDM (Mobile Device Management) solutions and disallow BYOD (Bring Your Own Device). Here, employees use only company issued devices, but organizations may still permit third-party applications. In such cases, every approved app release must be reviewed before deployment. Understanding what these apps store locally and whether they touch corporate data like emails/documents etc. becomes quite important.
3. Platforms and Marketplaces
Mobile applications often integrate deeply with an ecosystem when it comes to platform providers or marketplaces. These applications may access or even persist platform data on the device. Having zero visibility into how this data is handled, the risk of leakage grows significantly and can result in significant loss to marketplace providers.
The ever unsolved Local Storage Question
Across all these scenarios, one theme repeats: organizations need to know what is being stored locally and whether sensitive data is at risk.
In mobile applications, data isn’t always stored in plain text. Many applications use hashing, encoding, or even encryption which typically poses an identification challenge. While these methods may look like protection at first glance, they are not always implemented securely. In some cases: -
- Data might be encoded (e.g., Base64), but is easily reversible.
- Weak or custom encryption might give a false sense of security.
- Hashes might still leak valuable patterns or be vulnerable to brute force attacks.
When there is a large chunk of data in terms of device data or heavily loaded log files of the mobile application, manually identifying and validating sensitive data becomes extremely time consuming & inefficient. Due to his, it becomes crucial to introduce automated tools or scripts that can systematically find sensitive data in various storage formats.
A Quick Example
Consider a mobile application that saves the user's session token locally:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
This appears to be random text at first glance. It is actually a JSON Web Token (JWT) that is Base64-encoded. Due to this kind of encoding, anyone with access to the device can decode it and uncover: -
{
"user": "acme@acme.com",
"role": "admin",
"exp": "2025-08-31T23:59:59Z"
}
This shows that sensitive data, including roles, usernames, and token expiration dates, is being stored in local storage. If logs also capture this token (which happens more often than one can think), the exposure multiplies. Without automation, there is a high chance of missing out on spotting such patterns in logs.
Blueinfy’s Approach
At Blueinfy, we have taken a very focused approach to solving this problem. We developed a lightweight client-side mobile review framework that leverages internal technology and automation. Instead of duplicating heavy mobile product testing, our reviews target the most impactful risks:
- Sensitive Information stored in local storage
- Sensitive information left behind in logs (processed at scale using automation)
- Poor SharedPreferences usage and insecure storage practices
- Sensitive or private data sent to third parties
By combining automation scripts with targeted analysis, we can cut through massive logs, detect hidden storage of sensitive data, and flag cases where security controls (hash, encode, encrypt) don’t truly protect the data. The client-side mobile review framework is mainly developed keeping in mind the core problem of leakage of client/sensitive data.
Balancing Quality, Speed, and Cost
This approach allow us to achieve: -
• High-quality insights: We focus on the areas that matter most.
• Speed: In rapid agile cycles, automation enables quick reviews.
• Cost-effectiveness: Real risks being addressed in a fraction of traditional mobile testing costs.
Final Thoughts
In today’s mobile first world, API security is only one part of the story. To truly protect organizational data, companies must also review the mobile client surface, with particular attention to how and where data is stored locally.
At Blueinfy, our approach shows that with the right focus and automation, organizations can uncover risks hidden in storage and logs without sacrificing quality, speed, or cost.
Article by Hemil Shah