Key Takeaways:
- Sensitive data is most commonly exposed through unencrypted SQLite databases, misused preference storage, and log files
- The risk is often unintentional, with developers misunderstanding platform-specific storage behaviours being a leading cause of exposure
- Encrypting data at rest, using platform-native keystore APIs, and enforcing secure deletion on logout are the three highest-impact controls
- Independent penetration testing using static and dynamic analysis is the only reliable way to confirm that storage controls are working as intended
Introduction
Mobile applications handle enormous amounts of sensitive data, from user credentials and session tokens to payment details and personal information. However, many applications fall short when securing that data properly. This blog covers the most common mobile data storage risks that security leaders should monitor, and how penetration testing can surface insecure storage before a problem arises.
What Is Insecure Data Storage in Mobile Apps?
Insecure data storage in mobile apps occurs when mobile applications store sensitive data- credentials, tokens, Personally Identifiable Information (PII), financial data- in locations or formats accessible to unauthorised parties.
OWASP ranks insecure mobile data storage as the second most significant threat to mobile applications (OWASP Mobile Top 10, 2024), demonstrating just how prevalent this threat can be.
The risk doesn’t always stem from malicious intent. While deliberate misuse does occur, the more common culprit is developers inadvertently exposing sensitive data insecurely due to a misunderstanding of platform-specific storage behaviours: for example, incorrectly assuming that iOS Keychain or Android Keystore protections apply automatically, or failing to appreciate how accessible certain storage locations are to other applications or to physical device access.
However, unintentional data exposure is still data exposure, and mobile app developers must be vigilant that they are enforcing secure coding practices to protect sensitive data.
Where Do Mobile Apps Store Data and Why Does It Matter**?**
Mobile applications rely on several native storage mechanisms to store data locally, and each carries its own security implications. Understanding where sensitive data ends up, and how accessible those locations are is the first step in identifying insecure local storage mobile application risks and preventing attackers from accessing stored data.
SQLite Databases and Local Files
SQLite databases and local file directories are among the most common storage locations in mobile devices. On rooted or jailbroken devices, unencrypted databases are trivially accessible using basic forensic tools. Data written here is frequently overlooked by developers once the feature is shipped, leaving sensitive records exposed indefinitely.
SharedPreferences and NSUserDefaults
SharedPreferences on Android and NSUserDefaults on iOS are routinely misused to store tokens, user credentials, and session identifiers that have no place in general-purpose preference storage. These mechanisms write plain XML or plist files to disk, which are readable without special privileges on any compromised device.
Application Logs and the Clipboard
Sensitive data frequently leaks into crash log files and debug outputs, persisting long after a session has ended and surfacing in places developers never intended.
Clipboard data presents a similar risk: historically, any application running on the device could silently read clipboard contents, making it a common vector for mobile app data storage security failures and unauthenticated data access.
It is worth noting that both iOS 12+ and Android 12+ have introduced controls to address this. iOS restricts clipboard access more aggressively in recent versions, whilst Android now notifies users when an app reads clipboard content. However, these mitigations are version-dependent and do not eliminate the risk, particularly across older devices or unmanaged fleets.
But how does improperly storing sensitive information in your mobile applications lead to potential breaches? Let’s cover some common risks of insecure mobile application data storage and how internal storage can be exploited.
The Risks of Storing Sensitive Data Insecurely in Mobile Apps
Insecure data storage in mobile apps introduces unique risks for organisations. Beyond the initial risk of attackers exploiting sensitive user data, this information can then be exploited further to enact credential theft, PII exposure, third-party SDK data leakage, and identity theft.
| Threat vector | How it escalates | UK GDPR exposure | Business outcome |
|---|---|---|---|
| Sensitive user data exploitation | Initial compromise creates the foundation for all downstream attacks. Attackers map data structures, identify high-value accounts, and stage further intrusions. | Failure to implement appropriate technical and organisational security measures risks fines up to £17.5M or 4% of global annual turnover. | Regulatory investigation triggered; mandatory breach notification to the ICO within 72 hours; potential class-action liability from affected individuals. |
| Credential theft | Stolen credentials enable account takeover, lateral movement across systems, and privilege escalation, turning a single breach into an enterprise-wide incident. | Inadequate access controls and failure to implement data protection by design. | Operational disruption across affected systems; forensic investigation costs; potential loss of cyber insurance coverage. |
| PII exposure | Exposed personally identifiable information gives attackers sufficient data to launch social engineering campaigns or commit fraud in users’ names. | Especially severe where special category data is involved. The ICO has issued fines exceeding £4.4M for large-scale PII breaches. | Reputational damage compounded by media coverage; user churn as affected individuals migrate to competitors; long-tail legal costs from individual compensation claims. |
| Third-party SDK data leakage | Compromised or misconfigured SDKs silently exfiltrate user data to external endpoints, often evading standard detection. Supply chain risk extends the attack surface beyond direct control. | Organisations remain fully liable for data processed by third-party processors. Insufficient vendor due diligence constitutes a violation in its own right. | Loss of user trust where SDK leakage is disclosed publicly; supplier contract disputes; reputational damage extends to third-party vendors. |
| Identity theft | Aggregation of stolen credentials and PII enables full synthetic identity fraud, with attackers impersonating users across financial and government services. | The downstream harm to data subjects is treated as an aggravating factor in ICO penalty calculations. | Severe, long-term reputational damage; increased regulatory scrutiny; and affected users may suffer years of financial and personal harm, leading to higher compensation claims. |
How Do Attackers Exploit Mobile App Data Storage?
Mobile app data breaches can be achieved by attackers in several ways, with this approach determined by the mobile device type hosting the application, (e.g. Apple or Android apps), the device’s file system, and subsequent vulnerabilities that are unique to each.
Here’s how attackers will typically exploit mobile app data storage:
Physical and Device-Level Attacks
Attackers with physical access to a device can use USB extraction tools and forensic imaging software to pull raw data directly from storage. Stolen or unattended devices are the most common entry point. Encryption at rest is the primary defence against this attack class.
Runtime and Network-Based Exploitation
Dynamic analysis tools allow attackers to intercept data as it is written to storage during live app execution. This bypasses static protections and captures sensitive information at the moment it is most exposed.
Unencrypted app data can also be pulled from device backups using native utilities such as Android’s adb backup or Finder on macOS for iOS devices, requiring no specialist tooling and accessible to low-sophistication attackers.
How to Secure Data Storage in Mobile Applications
While pentesting is a vital component of ensuring your mobile application storage is robust, it’s also important that businesses enforce internal controls to store sensitive data securely.
Taking a proactive approach always offers stronger protection than reacting to breaches after they occur.
Here are some key controls to consider to secure data transmission and enforce proper access controls:
| Control | What it does | Why it matters |
|---|---|---|
| Encrypt data at rest | Applies AES-256 or platform-native encryption to all locally stored files, databases, and caches | Renders extracted data unreadable without the key, protecting against physical device compromise and forensic extraction. Restricts access to malicious actors |
| Avoid storing sensitive data locally where avoidable | Relies on server-side retrieval instead of persisting sensitive data; enforces short TTLs on cached tokens | Data that does not exist on the device cannot be stolen from it, reducing the blast radius of any storage compromise and minimising security vulnerabilities |
| Implement secure deletion on logout | Overwrites or cryptographically erases sensitive files and database rows on user logout or session expiry | Prevents recovery of stale session artefacts via file-system carving or unallocated cluster inspection |
| Sanitise logs in production builds | Strips or redacts sensitive values from log output before release builds ship | Prevents credentials, tokens, and PII from leaking through device logs accessible to other apps or via USB debugging |
| Restrict backup inclusion of sensitive files | Excludes sensitive files from OS-managed backups using platform flags | Prevents sensitive data from being exfiltrated via cloud backup channels or device-to-device transfer flows |
Strong encryption algorithms and proper input validation are essential proactive measures in defending your mobile applications from potential threats. Robust authentication mechanisms work alongside these controls to ensure that only verified users can access protected data in the first place, because encryption alone cannot compensate for an identity layer that can be bypassed.
Securing how your application verifies who someone is, and maintaining that assurance throughout a session, is where storage security and access control meet.
Securing User Credentials with Authentication Controls
| Control | What it does | Why it matters |
|---|---|---|
| Validate credentials server-side | Authenticates users against a secure backend endpoint over TLS; never validates passwords locally against a stored hash on the device | Prevents offline brute-force attacks and ensures revocation is immediate when credentials are compromised |
| Use platform biometric APIs | Delegates fingerprint and face authentication to OS-managed APIs (Face ID, Android BiometricPrompt) rather than custom implementations | Biometric data never leaves the secure enclave; platform APIs handle liveness detection and retry lockout by default |
| Implement token-based sessions | Issues short-lived access tokens and longer-lived refresh tokens post-authentication; stores both exclusively in the platform keystore | Limits the window of exposure if a token is intercepted; refresh tokens can be revoked server-side without requiring re-entry of credentials |
| Enforce multi-factor authentication | Requires a second factor (TOTP, push notification, or hardware key) in addition to a password for sensitive operations | Credential theft alone is insufficient to gain access; it significantly raises the cost of account takeover |
| Lock out after failed attempts | Enforces progressive delays or a hard lockout after a configurable number of failed authentication attempts | Prevents brute-force and credential-stuffing attacks against the login flow |
How OnSecurity Helps Secure Mobile App Data Storage
Data theft often starts with sensitive information left unprotected on a user’s device. Protecting this data requires more than just following best practices; it needs independent testing to ensure your security measures are effective.
OnSecurity’s mobile application penetration testing surfaces mobile application data storage vulnerabilities before attackers can exploit them. Using a combination of static and dynamic analysis, testers examine your application as both an unauthenticated observer and an authenticated user, checking for plaintext credentials written to disk, unprotected local databases, tokens that persist beyond logout, and sensitive values leaking into production logs.
Testing is delivered through OnSecurity’s platform-based, CREST-certified service, meaning findings are documented clearly, severity is rated consistently, and retesting is built into the process so you can confirm that fixes have landed correctly. For more detailed information on the testing itself, check out our blogs on mobile application testing for iOS and Android.
Stay ahead of attackers and protect your users’ data today with OnSecurity’s mobile application penetration testing services.
