Secure mobile payment apps: What devs need to know now

By Sergio Castell

Mobile payments security is a competitive differentiator that underpins market viability, user trust, and brand integrity.

Mobile payment apps have evolved from yesterday’s novelty to today’s critical infrastructure. They now process transactions that drive industries and personal lives, from rideshares to retail checkouts. For mobile payment app developers, this shift makes app security a high-stakes call to action where security is the make-or-break element.

Despite this, the attack surface for mobile payment apps continues to expand, facing threats ranging from code tampering and reverse engineering to API abuse and overlay attacks. As threat actors refine their tradecraft, developers must evolve from a reactive, checklist-driven security posture to one where security is embedded throughout the Software Development Lifecycle (SDLC).

From retrofit to proactive: The threat modeling imperative

Retrofitting security post-development is a recipe for failure. Developers should begin threat modeling early, identifying where sensitive data lives, how it flows, and where it’s vulnerable to interception or manipulation.

Modern threat actors don’t need physical access to a device to launch an attack. Their goal is to steal scalable assets, including credit card data, Personally Identifiable Information (PII), cryptographic keys, and even the application’s source code. They often use two primary methods:

• Repackaging: Decompiling your app, injecting malicious code, and redistributing it to intercept data or manipulate transactions.
• Runtime instrumentation: Using tools like Frida and Xposed to hook into a running app, alter its logic, and bypass security controls in real time.

The barrier to entry for reverse engineering is alarmingly low due to the proliferation of free-to-use tooling. So the question you need to ask yourself is, what would an attacker find? Hardcoded keys? Flaws in your authentication logic? A single vulnerability in the client can be enough to compromise your entire user base and inflict significant damage to your brand.

The client-side blind spot: Hardening the mobile attack surface

This ease of reverse engineering highlights a critical, often-overlooked domain: the client itself. APIs are the backbone of mobile payments, enabling identity verification, transaction processing, and communication with banking systems. Developers often focus on securing these endpoints with encryption, tokens, and rate limits. But if the client-side app isn’t hardened, these backend defenses can be bypassed by attackers who impersonate legitimate users or abuse your API endpoints directly.

Different app architectures present unique risks. Mobile wallets are often targeted for secure storage breaches and the extraction of communication keys. SoftPOS mobile apps, meanwhile, face threats from misconfigured intents, weak inter-process communication (IPC), and a lack of TLS pinning. Client-side protections, such as TLS/certificate pinning and jailbreak/root detection, are vital to ensuring that your APIs are not being called from a compromised environment.

Build for Zero Trust on the client

The principle of Zero Trust applies directly to mobile: never trust the runtime environment. A user’s device can be compromised, and malicious apps can coexist alongside yours.

To counter this, implement Runtime Application Self-Protection (RASP). RASP acts as a real-time defense mechanism inside your app, detecting and blocking threats like debugging, screen readers, and code injection as they happen. For storing critical assets, go beyond standard encryption. Protect sensitive data like cryptographic keys by using strong obfuscation and, where possible, binding them to hardware-backed secure components like a Trusted Execution Environment (TEE) or Secure Element.

From compliance to resilience

It’s not just about user trust. To launch a payment app, you must undergo rigorous security assessments guided by standards from organizations like EMVCo and the PCI SSC. This process involves penetration testing by certified labs and addressing all found vulnerabilities before going to market.

But compliance is the floor, not the ceiling. These certifications are a snapshot in time, while threats constantly evolve. Every payment app has a unique risk profile based on how it handles PINs, uses biometrics, or integrates with hardware. Create a bespoke threat model that guides your security efforts. Frameworks like the OWASP Mobile Application Security Verification Standard (MASVS) can complement payment-specific regulations by helping you build holistic security, from secure coding to runtime defenses.

A proactive security culture

Ultimately, securing mobile payment apps demands a culture shift. Adopting DevSecOps principles means security can no longer be siloed to a single phase of the SDLC or relegated to a compliance checklist.

Development teams must be trained to think securely, empowered to evaluate third-party SDKs, and incentivized to prioritize protection alongside performance and usability.

Adopt a continuous, multi-layered strategy:

• Test relentlessly: Combine automated scans in your CI/CD pipeline with thorough manual penetration tests before each release.
• Enforce updates: Prevent users from using outdated, vulnerable versions of your app. Implement a mechanism to require updates to ensure security patches are deployed widely.
• Obfuscate your code: Strong code obfuscation and anti-tampering measures protect the running app and significantly raise the bar for attackers trying to reverse-engineer it.
• App Attestation: Verify that only your genuine app can access your APIs to block clones, bots, and other unauthorized clients from exploiting backend logic or causing service disruptions.

As attackers continue to innovate, so too must our defenses. In the competitive mobile payments landscape, robust security is no longer just a defensive posture — it is a competitive differentiator that underpins market viability, user trust, and brand integrity. The stakes are too high for anything less.