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SUZU Offensive Security Solutions

Client-Server Application Testing

Not every application runs in a browser. Suzu Labs tests thick-client and desktop applications the way real attackers do, reversing binaries, intercepting client-server communications, bypassing the client to attack the backend directly and proving what happens when the client is under the attacker's control.

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Client-Server Application Testing Services

When the Client Is the Attack Surface

Thick-client applications present a fundamentally different risk profile than web or mobile apps. The client binary runs on hardware the attacker controls, business logic often lives client-side, and communication with backend services may rely on protocols that aren't HTTP and aren't designed for hostile environments.

We test the full stack: the client binary, the data it stores locally, the protocols it uses to communicate, and the backend services it depends on. If your application has a desktop installer, a fat client, or a client-server architecture, this is the engagement you need.

Download the Pentest Sourcing Guide
Client Server Testing

How We Test Client-Server Applications

From Binary to Backend

We assess every layer of the client-server stack, from the installed binary on the endpoint to the backend services it trusts.

Binary Analysis & Reverse Engineering

We decompile and reverse-engineer the client application to identify hardcoded credentials, embedded API keys, disabled security controls, and business logic that can be manipulated by modifying the binary.

Learn more about reverse engineering

Client-Server Communication

We intercept, decode, and manipulate traffic between the client and server, testing custom protocols, proprietary serialization formats, and encrypted channels for authentication bypass and data tampering.

Learn more about protocol testing

Local Data & Credential Storage

We assess how the application stores data on the endpoint: configuration files, local databases, cached credentials, temp files, and registry entries that could enable account takeover or privilege escalation.

Learn more about data storage risks

Authentication & Session Handling

We test how the client authenticates to the server, how sessions are maintained, and whether an attacker can replay, forge, or hijack sessions to access other users' data or escalate privileges.

Learn more about authentication testing

Backend Service Trust


Many thick clients trust the server implicitly, and many servers trust the client. We test both directions: can a modified client trick the server into unauthorized actions, and can a rogue server compromise the client?

Learn more about trust validation

Update & Deployment Mechanisms

We evaluate how the application receives updates, whether update channels are authenticated and encrypted, and whether an attacker could deliver a malicious update to endpoints through a compromised or spoofed update server.

Learn more about supply chain risks
Pass Your Next Audit With Confidence

Penetration Testing

Companies turn to pentesting when they need real answers, not assumptions.
Maybe a customer is asking for proof, a compliance requirement is coming up, or they simply want to know if they’re actually protected.

Suzu Labs safely tests your systems the way a real attacker would, so you can see where things could break before it becomes a real problem.

  • Meet requirements for frameworks like SOC 2, ISO 27001, HIPAA, and PCI DSS with real, defensible testing, not just automated scans.
  • Show clients, vendors, and stakeholders that your security has been tested by real experts, not just assumed to be secure.
  • Turn one-time testing into ongoing validation so your security keeps up with new threats, not just audit cycles.
  • What We Test: Web-App, Mobile App, API, External Network, Internal Network, WIFI, Cloud, IoT, Physical.
See How Modern Pentesting is Changing → Need a Pentest?
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PHYSICAL LAYER DEFENSE

Hardware Hacking

This usually comes up when something is on the line. A new device launch, customer trust, or protecting intellectual property.

We evaluate the security of your hardware and embedded systems to ensure they can’t be easily exploited, cloned, or manipulated in the real world.

  • When you’re shipping devices or relying on connected technology, unseen risks can lead to real consequences. From customer trust issues to expensive fixes. We help you catch those issues before they impact your business.
  • What We Hack: SCADA, IoT, OT, Vehicles, Embedded Systems.
Hardware Hacking in Action → Need Hardware Hacked?
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Questions

Client-Server Application Testing Answered

Any application with a client component installed on an endpoint that communicates with a backend server. This includes desktop trading platforms, ERP clients, medical device management consoles, point-of-sale systems, engineering and CAD tools, legacy enterprise software, and custom internal business applications that aren't browser-based.


Web application testing targets applications that run in a browser over HTTP. Client-server testing targets applications with installed client binaries that may use custom protocols, proprietary data formats, and client-side business logic that don't exist in a web context. The attack surface is fundamentally different: the attacker controls the client binary, can reverse-engineer it, modify it, and manipulate its communication with the server in ways that aren't possible with a browser-based application.


Yes. We test the full stack. The client binary, its local data storage, the communication channel, middleware layers, and the backend services it connects to are all in scope. If the architecture includes middleware such as message brokers, application servers, or API gateways between the client and the database tier, we test those trust boundaries as well. If the backend also exposes APIs used by other clients (web, mobile), we can coordinate with a broader application testing engagement to cover the full surface.

 

We reverse-engineer proprietary protocols as part of the engagement. We intercept traffic, analyze the serialization format, map the message structure, and build custom tooling to replay, modify, and inject messages. Undocumented protocols are not a barrier to testing; they're often where the most significant findings live because they've never been subjected to adversarial scrutiny.

 

We need the client application installer or binary, test accounts at each user role, access to a test or staging server environment, and any available documentation on the application architecture. If the application requires specific licensing, hardware dongles, or environment configuration, we coordinate that during scoping so testing can start without delays.

Most engagements run two to three weeks depending on the complexity of the client binary, the number of communication protocols, and how many user roles need testing. Binary reverse engineering and custom protocol analysis can extend timelines for particularly complex applications. We provide a clear timeline during scoping, and if we discover a critical finding that poses an imminent threat, we escalate it to your team immediately.


We strongly prefer testing against a staging or test environment that mirrors production. If production testing is required (for example, when no staging equivalent exists or when testing needs to validate real infrastructure), we coordinate safe windows, use non-destructive techniques, and add guardrails to minimize operational risk.


The report is the beginning, not the end. You get a live debrief with the operators who ran the engagement, walking through every finding, its real-world impact, and specific remediation steps. If your team needs hands-on help remediating, we can work alongside your engineers to close the gaps. Once fixes are in place, we conduct retesting to verify they're resolved.

Client-Server Application Testing vs. Web Application Pentesting

Client-Server Application Testing Web Application Pentesting
Scope Desktop applications, thick clients, custom protocols, local data storage, binary analysis, backend services Browser-based applications, HTTP/HTTPS traffic, APIs, session handling, business logic
Attack Surface Client binary, local file system, registry, memory, custom protocols, client-server trust boundaries Web forms, cookies, session tokens, API endpoints, client-side JavaScript, server-side logic
Common Vulnerabilities Hardcoded credentials, insecure local storage, protocol manipulation, client-side logic bypass, update mechanism abuse SQL injection, XSS, CSRF, broken access controls, business logic flaws, insecure API handling
Testing Approach Binary reverse engineering, protocol interception and manipulation, memory analysis, runtime modification Simulated attacks through the browser and API layer targeting application workflows and data handling
Impact if Compromised Credential theft, unauthorized backend access, data manipulation, lateral movement via compromised endpoints Data breach, account takeover, unauthorized transactions, customer data exposure
Ideal For Organizations with desktop applications, trading platforms, ERP clients, medical device software, POS systems, or legacy client-server architectures Organizations operating SaaS platforms, customer portals, e-commerce sites, or browser-based business applications

Verified expertise

Validate defenses. Reduce exposure.

Penetration Testing

What It Is: We don't just scan for vulnerabilities; we exploit them safely to prove where your defenses might fail. Our offensive security experts simulate real-world attacks to identify complex misconfigurations and logic flaws across your entire infrastructure.

 

  • Full-Spectrum Testing: Deep dives into web apps, internal/external networks, and cloud environments.
  • Risk-Based Analysis: Understand exactly how an attacker could move laterally through your systems.
  • Continuous Validation: Transition from periodic "check-the-box" audits to a culture of constant defensive improvement.
  • What We Test: Web-App, Mobile App, API, External Network, Internal Network, WIFI, Cloud, IoT, Physical.
Watch how modern pentesting is changing → Need a Pentest?
ChatGPT Image Apr 17, 2026, 01_54_29 PM
PHYSICAL LAYER DEFENSE

Hardware Hacking

What It Is: Modern attacks don’t stop at software. We analyze firmware, embedded systems, and IoT devices to uncover security gaps at the hardware level. From side-channel testing to reverse engineering, our hardware security services safeguard critical infrastructure and consumer technology alike.

  • Move beyond software patches by identifying vulnerabilities in firmware and embedded systems that traditional scanners miss, ensuring your hardware is secure from the first boot.
  • We simulate advanced attack vectors like side-channel analysis and reverse engineering to ensure your critical infrastructure and consumer tech can withstand hands-on exploitation.
  • Protect your brand and your users by uncovering hidden gaps in interconnected devices, preventing your hardware from becoming an easy entry point for larger network breaches.
  • What We Hack: SCADA, IoT, OT, Vehicles, Embedded Systems.
Hardware Hacking in Action → Need Hardware Hacked?
person hacking hardware
OFFENSE AND DEFENSE SYNERGY

Purple Team Exercises

What It Is: High-impact collaborative engagements where our offensive experts (Red) and defensive (Blue) teams work side by side to test detection and response capabilities, turning findings into immediate improvements.

  • Targeted Exploitation: We move beyond basic scanning to emulate specific TTPs (Tactics, Techniques, and Procedures) used by modern threat actors, ensuring your defenses are tested against actual adversary behavior.
  • Closing the Detection Gap: By mapping offensive actions to your specific security telemetry in real-time, we identify exactly where visibility fails and provide the code-level fixes to bridge those gaps.
  • Operational Resilience: We don't just find vulnerabilities; we use offensive data to build "detection-as-code," giving your team the playbooks needed to stop sophisticated lateral movement and data exfiltration.
Why Purple Teaming Outperforms Traditional Testing →
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PROVING DEFENSIVE EFFICACY

ThreatSIM — Attack Simulation & Service Validation

What It Is: ThreatSIM is our proprietary platform designed to simulate MITRE ATT&CK®–based adversary behaviors safely within client environments. Unlike point-in-time tests, ThreatSIM continuously validates the effectiveness of your security stack, your SOC, and your MSSP’s detection and response capabilities.

  • Move beyond static testing with ongoing simulations that verify your security stack, SOC, and MSSP are detecting and blocking threats in real time.
  • Safely emulate real-world adversary behaviors within your environment to ensure your defenses are tuned against the most current and relevant global attack tactics.
  • Eliminate guesswork by gathering concrete data on how well your existing tools and service providers perform, allowing you to bridge gaps before a real breach occurs.
Validate My Security Stack See ThreatSIM in Action
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Book a threat briefing

If there’s a way in, we’ll find it first.

A patch is a start, but it isn't a strategy. Connect with our offensive security specialists to identify the logic flaws and lateral movement paths that put your critical assets at risk. Let’s build a roadmap to true resilience.

We'll be in touch within one business day to schedule your briefing. No sales follow-up sequence — just the briefing.

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