For a fintech company or e-wallet provider, the mobile application is only the visible part of a much larger technology environment. Behind every balance check, fund transfer, bill payment, account registration, beneficiary addition, card transaction or wallet top-up, several systems may be communicating through APIs, authentication services, databases, payment gateways, identity platforms and third-party integrations. This interconnected architecture makes digital financial services convenient, but it also creates a large attack surface. An attacker does not necessarily need to compromise the entire banking infrastructure to cause damage. A weakness in an API authorization check, an insecure mobile session, exposed credentials, poorly protected transaction flow or vulnerable third-party integration may be enough to access customer information or manipulate a financial process. For fintechs and e-wallet providers, security testing therefore needs to go considerably deeper than checking whether the mobile app uses HTTPS or whether a vulnerability scanner finds outdated software. The real objective is to test whether the complete transaction journey remains secure when someone deliberately attempts to bypass the assumptions built into it.
OWASP maintains separate security standards for these two major areas. Its API Security Top 10 identifies risks such as broken object-level authorization, broken authentication, unrestricted access to sensitive business flows, security misconfiguration and unsafe consumption of third-party APIs. Its Mobile Application Security Verification Standard, or MASVS, covers areas including storage, cryptography, authentication, network communication, platform interaction, code security, resilience and privacy. For fintechs, the strongest testing program considers both surfaces together because a secure-looking mobile application can still communicate with an insecure API, and a well-designed API can still be exposed through weaknesses in the mobile client.
Why Financial Apps Require Deeper Security Testing
Financial applications have a characteristic that makes security failures particularly serious: many of the actions available to legitimate users directly affect money, identity or sensitive financial information. If an attacker compromises a social-media account, the consequences may be significant. If the same attacker compromises a digital wallet, they may potentially attempt unauthorized transfers, change beneficiary information, abuse payment flows, access identity documents or manipulate transactions.
This means security testing must evaluate not only traditional technical vulnerabilities but also business logic. Consider a wallet transfer. A legitimate transaction might require the user to authenticate, choose a beneficiary, enter an amount, confirm the transaction and provide an additional verification factor. Every step appears secure when used normally.
A security tester asks different questions. Can the amount be changed after confirmation? Can the beneficiary identifier be modified directly in the API request? Can the confirmation request be replayed? Can the same transaction be submitted twice? Can one user’s transaction identifier be replaced with another user’s identifier? Can rate limits be bypassed? Can the app be tricked into skipping one stage of the transaction workflow? These are not necessarily vulnerabilities that a standard automated scanner will discover. They require understanding how the financial process is supposed to work and then attempting to violate those assumptions.
API Authorization Should Be One of the First Areas Tested
Authorization weaknesses are among the most important API risks for fintech platforms. An application may correctly confirm that a user is logged in while still failing to confirm whether that user is authorized to access a particular object or function. Imagine an API request that retrieves a transaction:
/api/transactions/45872
If the authenticated user changes 45872 to another transaction number, what happens? A secure system should confirm that the requested transaction actually belongs to the authenticated customer. If it only checks that the customer is logged in, one user may potentially access another user’s information. OWASP identifies this class of weakness as Broken Object Level Authorization, or BOLA, and places it prominently in its API Security Top 10. OWASP also distinguishes function-level authorization problems, where a user may be able to access administrative or higher-privilege operations that should not be available to their role.
For fintech applications, authorization testing should therefore extend across customer profiles, wallet balances, transaction histories, cards, beneficiaries, KYC records, payment instruments, disputes, refunds and administrative functions. Every API operation that references an object needs to answer two separate questions: Who is making this request, and are they allowed to perform this specific action on this specific resource?
Authentication Testing Must Go Beyond the Login Screen
A successful login is only the beginning of authentication security. Fintechs should test the complete identity lifecycle, including registration, login, password reset, PIN changes, OTP verification, Multi-Factor Authentication, account recovery, device registration, session renewal and logout. Password-reset and account-recovery processes deserve particular attention because attackers often target the weakest way into an account rather than the strongest. For example, a wallet may have strong MFA during normal login but allow a weaker recovery process based on information that can be obtained through social engineering. In that situation, the recovery mechanism effectively becomes the true security boundary.
Session and token handling also need careful testing. Security teams should examine whether authentication tokens expire appropriately, whether logout invalidates active sessions where required, whether tokens can be replayed from another device, whether refresh tokens are securely handled and whether high-risk actions require additional verification. Authentication controls should also be evaluated against brute-force attacks, credential stuffing and automated account takeover attempts. A login interface that technically works correctly may still be vulnerable if an attacker can submit thousands of password attempts without meaningful restrictions.
Transaction Logic Needs Its Own Security Test Plan
Traditional application testing often concentrates on technical vulnerabilities. Financial applications require additional attention to transaction logic.
Security testers should examine how the platform validates the amount, source account, beneficiary, currency, transaction type, transaction limits and authorization state. A critical principle is that the backend should not blindly trust values supplied by the mobile application. The mobile application runs on a customer’s device, which means an attacker may be able to intercept, modify or recreate the requests it sends. Hiding a field in the mobile interface does not make that field secure.
Suppose an application prevents transfers above PKR 100,000 through its user interface. If the limit is enforced only in the mobile application, an attacker may attempt to alter the API request and submit PKR 500,000 directly. The server must independently enforce the rule.
The same principle applies to transaction fees, wallet balances, beneficiary status, discounts, cashback, payment limits and other business rules. Testing should also cover duplicate and replayed transactions. If a legitimate payment request is captured and submitted again, does the system recognize that the transaction has already been processed? Financial APIs often need mechanisms such as unique transaction references, nonces, timestamps or idempotency controls to prevent unintended duplicate processing. The exact implementation varies, but the security requirement remains the same: one authorized action should not accidentally become multiple financial actions.
Sensitive Data Should Be Tested Across the Entire Journey
Financial applications process sensitive information in several locations. Data may exist on the mobile device, travel across networks, appear in API responses, reach backend systems and be shared with approved third parties. Testing therefore needs to evaluate data throughout its lifecycle. On the mobile side, testers should examine whether credentials, tokens, account information or other sensitive data are stored insecurely in local databases, preferences, logs, cache files, screenshots or backup locations. OWASP MASVS specifically treats secure data storage, cryptography, authentication and secure network communication as distinct control areas because protecting sensitive data requires more than one mechanism. API responses should also be examined for excessive information. An application may need a customer’s name and account status but receive a much larger data object containing information that is never displayed in the interface. An attacker who can inspect API traffic may gain access to this unnecessary information. A useful security principle is simple: if the client does not need the data, the API should reconsider sending it.
Logs deserve similar attention. Production systems should not expose authentication tokens, complete payment information, passwords, PINs or other sensitive values through application logs, debugging output or error responses.
Mobile Device Storage and Application Behaviour Must Be Tested
The mobile application itself creates risks that do not exist in a traditional browser-only environment. Applications may store information locally for performance or convenience. Testers therefore need to inspect application files, local databases, preferences, cached information and other device storage areas. On Android and iOS, platform-specific security features can help protect sensitive information, but developers still need to use them correctly. The test should also examine what happens when the application moves into the background. Could sensitive account information appear in the operating system’s recent-app preview? Are screenshots permitted on highly sensitive screens when the risk profile suggests they should be restricted? Does copied information remain unnecessarily available in the clipboard?
Application permissions should also be reviewed. A financial app should not request access to device functionality without a legitimate requirement. Excessive permissions increase both privacy risk and potential attack surface. Deep links, custom URL schemes and interactions with other applications also require testing because poorly validated links may allow attackers to manipulate application navigation or pass unexpected data into sensitive application functions.
Encryption Should Be Tested, Not Assumed
Seeing HTTPS in an application does not automatically prove that communication is secure. Security teams should test how TLS is configured, whether certificate validation is functioning correctly, whether weak protocols or configurations remain enabled and whether sensitive traffic can be intercepted under realistic attack scenarios. Cryptographic implementation inside the application should also be reviewed.
Developers sometimes attempt to create custom encryption algorithms, hard-code keys inside the application or embed secrets directly into mobile code. This creates problems because mobile applications can be downloaded and analyzed by attackers. If a secret is shipped inside the application package, security teams should assume that a sufficiently motivated attacker may eventually discover it. Cryptographic keys, API credentials and signing secrets therefore require appropriate architecture and lifecycle management rather than simple obfuscation.
Reverse Engineering and Application Tampering Matter for Fintechs
Unlike backend software, a mobile app is distributed directly to customers. An attacker can obtain the application package and examine it in a controlled environment. They may attempt to decompile code, inspect embedded strings, identify API endpoints, understand transaction logic, locate hard-coded secrets or modify application behaviour. OWASP MASVS includes resilience against reverse engineering and tampering as one of its mobile-security control groups.
For fintech applications, testers should therefore examine whether sensitive implementation details are unnecessarily exposed and whether tampering controls are proportionate to the threat model.
Techniques such as code obfuscation, anti-tampering measures and runtime integrity checks can increase attacker effort, but they should not become substitutes for secure server-side controls. A mobile application should never rely on the assumption that its code cannot be inspected or modified.
The backend should remain secure even if the attacker fully understands how the client works.
Rooted and Jailbroken Devices Need a Risk-Based Approach
Fintech applications often detect rooted Android devices or jailbroken iPhones because those environments may allow attackers greater control over application execution. Testing these controls can be useful, but organizations should avoid treating root or jailbreak detection as the primary security mechanism. Detection can sometimes be bypassed. More importantly, critical security decisions such as whether a transaction is authorized should remain enforced on trusted backend infrastructure. Device-risk information can be one component of a broader fraud and security model, alongside device binding, authentication strength, behavioural signals, transaction risk and account history. The principle is to use device security as an additional layer rather than placing complete trust in the mobile device.
API Rate Limits and Automated Abuse Need Serious Testing
Fintech APIs are attractive targets for automation. Attackers may attempt credential stuffing, OTP guessing, account enumeration, mass registration, promotional abuse or repeated transaction requests at machine speed. OWASP’s API Security Top 10 includes unrestricted resource consumption and unrestricted access to sensitive business flows, reflecting the risk created when important API functions can be automated without adequate controls. Rate limiting should therefore be tested across more than the login endpoint. OTP generation and verification, password recovery, beneficiary creation, wallet transfers, promotional codes, payment requests and account-registration processes may all need appropriate abuse controls. Testing should also determine whether limits can be bypassed by changing IP addresses, accounts, headers, devices or other request attributes. The objective is not simply to prevent high traffic. It is to prevent legitimate business functionality from being weaponized through automation.
API Inventory and Old Versions Can Create Hidden Exposure
Fintech development teams frequently update APIs as applications evolve. Version 1 becomes version 2. Testing endpoints remain temporarily accessible. Old mobile applications may continue communicating with legacy services. Over time, organizations can accumulate APIs that security teams no longer realize are publicly reachable. OWASP identifies improper API inventory management as a major API security risk because undocumented hosts, deprecated API versions and exposed testing endpoints can leave older security weaknesses available to attackers. Security testing should therefore include API discovery and inventory validation. Organizations should know which APIs are internet-facing, which versions remain active, which environments are accessible and who owns each service. A perfectly secured current API does not protect an abandoned API endpoint still connected to the same customer database.
Third-Party APIs Should Not Automatically Be Trusted
Fintech platforms rarely operate alone. They may communicate with banks, identity-verification providers, payment gateways, telecom operators, card processors, notification services, analytics providers and other external platforms. Developers can sometimes treat data from a trusted partner as inherently safe. OWASP specifically identifies unsafe consumption of third-party APIs as a security risk. Fintech applications should validate external data, handle failures securely, protect credentials used for integrations and monitor unusual behaviour across third-party connections. The organization should also consider what happens if the external service itself is compromised. A supplier relationship does not eliminate the need for security validation.
Mobile App Testing and API Testing Should Be Connected
One of the biggest weaknesses in application-security programs is testing the mobile application and backend API as separate systems. An attacker does not respect that division. A tester may begin inside the mobile application, capture its API requests, modify transaction parameters and then interact directly with backend endpoints. The mobile app may reveal undocumented API routes. API responses may expose information that helps reverse-engineer the client. A weak device-binding mechanism may allow a stolen token to be reused through a custom script. The security assessment should therefore follow complete attack paths. Instead of asking only whether the mobile app is secure or whether the API is secure, fintechs should ask whether an attacker can move between the two surfaces to compromise a financial process.
Testing Should Include Both Automated and Manual Techniques
Automated vulnerability scanning remains useful, but it is not sufficient for high-risk financial applications. Scanners are good at identifying certain known technical weaknesses, outdated components, insecure headers or obvious misconfigurations. They are much less effective at understanding business rules. A scanner may not recognize that customer A can access customer B’s wallet history by changing an identifier. It may not understand that a transaction can be replayed. It may not know that a supposedly one-time promotional credit can be claimed repeatedly through a specific sequence of requests. These weaknesses require manual security testing. A strong mobile and API VAPT engagement therefore combines tools with human analysis. The tester needs to understand how the application works, how users are supposed to move through financial processes and what security assumptions exist at each stage.
Security Testing Should Be Part of the Development Lifecycle
Waiting until immediately before release to test a fintech application creates unnecessary risk. If serious authorization or architectural problems are discovered at the end of development, fixing them can require significant changes. Security should instead be integrated throughout the software-development lifecycle. Threat modeling can identify likely attack paths during design. Secure code review can identify weaknesses during development. API and mobile security testing can validate controls before production. Dependency scanning can identify vulnerable third-party components. VAPT can provide independent validation before major releases or after significant architectural changes. Testing should also continue after launch. A mobile application that passed a penetration test last year may have received dozens of updates since then. New APIs may have been introduced. Dependencies may have changed. New attack techniques may have emerged. Security assurance therefore needs to follow the application lifecycle rather than being treated as a one-time certification exercise.
Pakistani Fintechs and Payment Institutions Also Need to Consider Regulatory Requirements
For Pakistani payment institutions, security testing also sits within a developing regulatory environment. The State Bank of Pakistan issued its Technology Risk Management Framework for Payment Institutions in October 2025 for Electronic Money Institutions, Payment System Operators and Payment Service Providers. The framework establishes baseline technology governance and cyber-risk requirements and required applicable institutions to comply by March 31, 2026. SBP explicitly describes the approach as risk-based and proportionate to the institution’s size, services and technology complexity. Not every fintech company falls into the same regulatory category, so organizations need to determine which SBP requirements actually apply to their business model. However, the direction is important. Financial technology organizations increasingly need to demonstrate that technology and cybersecurity risks are actively governed rather than addressed only when an incident occurs. Mobile app and API security testing should therefore form part of a wider technology-risk program that also includes governance, monitoring, incident response, access management, third-party risk and operational resilience.
What Should a Fintech Security Test Ultimately Prove?
A good security assessment should provide more than a long list of low-level vulnerabilities. It should help the organization answer practical questions. Can one customer access another customer’s information? Can authentication or account recovery be bypassed? Can transaction parameters be manipulated? Can transactions be repeated unexpectedly? Can privileged functions be reached by ordinary users? Can sensitive information be extracted from the mobile device? Can API tokens be stolen or reused? Can automated requests abuse business processes? Are outdated APIs still exposed? Are third-party integrations introducing unnecessary risk? Can attackers tamper with the application without important backend controls noticing? The answers should then be translated into remediation priorities based on technical severity and business impact. A vulnerability that exposes wallet balances or allows transaction manipulation deserves very different treatment from an informational issue with no realistic financial impact.
Final Thoughts
For fintechs and e-wallet providers, mobile app security and API security cannot be treated as separate checklists. The mobile application controls a highly sensitive customer experience, while APIs connect that experience with identity systems, balances, payment infrastructure, databases and third-party services. A weakness at either layer can undermine the security of the complete financial process. The strongest testing approach therefore examines authentication, authorization, transaction logic, data protection, session management, mobile storage, network communication, API inventory, rate limiting, third-party integrations, tampering resistance and backend enforcement as parts of one connected system. Most importantly, testers need to think like someone attempting to abuse the financial process rather than someone simply checking whether technical features are enabled. For fintechs, security is not proven because the app logs in securely or because an API uses HTTPS. Security is demonstrated when the entire transaction workflow continues enforcing the correct rules even when an attacker deliberately tries to manipulate it.
Test Your Fintech Applications and APIs With Ambsan Technologies
Ambsan Technologies helps organizations identify and validate security weaknesses across mobile applications, APIs, web applications, networks and supporting infrastructure through Vulnerability Assessment and Penetration Testing and broader cybersecurity assessments. For fintechs, e-wallet providers and digital-payment organizations, testing can focus on areas such as authentication, authorization, API security, transaction flows, mobile storage, session management, data exposure, business-logic abuse, third-party integrations and application infrastructure. The objective is not simply to produce another vulnerability report. It is to identify which weaknesses could create meaningful financial, customer or operational risk and provide clear remediation guidance.
Visit www.ambsan.com to discuss mobile application security testing, API security testing and VAPT requirements for your digital financial platform.