We are the backbone of engineers.

GMO Flatt Security, based in Tokyo, offers expert security assessments and penetration testing for software. Our seasoned professionals deliver proven, top-tier services. We also provide tools to help you internalize cutting edge, state of the art security practices.

Security Assessments & Penetration Testing

At the forefront of cybersecurity, we offer top-tier vulnerability assessments and penetration testing services conducted by world-class security engineers. Our expertise spans a wide range of targets, from web applications to IoT devices. We are adept at addressing security concerns unique to modern technology stacks, including serverless architectures and APIs leveraging GraphQL. You have our trust to safeguard your digital assets with cutting-edge, comprehensive security solutions.

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Takumi, an AI-Powered AppSec Auditor

Built by world-class offensive security experts, Takumi brings human-level reasoning to application security. Using a hybrid AI-powered SAST/DAST approach, it audits your code and live apps to uncover everything from classic vulnerabilities to logic flaws like broken authentication and authorization — all validated through safe exploit simulations for near-zero false positives.

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Meet the Experts

  • RyotaK

    Head of Security Research

    RyotaK is a security researcher known for his various groundbreaking cybersecurity research. His series of work has revealed critical vulnerabilities of cloud service providers including GitHub, Cloudflare, and other essential engineering platforms such as Homebrew and PyPI. He’s also known for participating in various live hacking events, winning multiple awards, and reporting vulnerabilities to many leading companies such as Google, Cloudflare, GitHub, Salesforce, and Microsoft.

  • Ryota Shiga

    Co-CTO

    Ryota Shiga is a well-versed security expert. He has revealed 15 critical vulnerabilities for the Linux Kernel and VMM (KVM/VirtualBox) during the 18 months of his research at GMO Flatt Security, all while directing over 100 web penetration testing projects, proving not only his extensive security knowledge but his leadership skills as well. He has also won a prize in Pwn2Own 2021 for reporting a privilege escalation in Ubuntu.

  • Takashi Yoneuchi

    Co-CTO

    Takashi Yoneuchi is one of the leaders of the cloud and application security industry in Japan with over 7 years of experience educating and motivating people on this topic. He is the author of "Web Browser Security" published in 2021, and more, with thousands of Japanese readers. He led Team Asia at the International Cybersecurity Challenge 2023 as Head Captain. He is also a member of the review board for CODE BLUE, the largest cybersecurity conference in Japan.

  • Shuta Ide

    Senior Security Engineer

    Shuta Ide is an offensive security specialist focusing on web applications, who has proven his elite skills by securing numerous first-place victories in CTF competitions, including SECCON CTF (domestic) in 2022 and 2024, the Japan Ministry of Defense CTF in 2021 and 2025, pbctf 2020, and IERAE CTF 2024.

Featured Projects

Beyond the Limit: Expanding single-packet race condition with a first sequence sync for breaking the 65,535 byte limit

BatBadBut: You can't securely execute commands on Windows

CVE-2025-59489: Arbitrary Code Execution in Unity Runtime

Clone2Leak: Your Git Credentials Belong To Us

Why XSS Persists in This Frameworks Era?

Beyond the Limit: Expanding single-packet race condition with a first sequence sync for breaking the 65,535 byte limit

BatBadBut: You can't securely execute commands on Windows

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Get in Touch

We'd love to hear from you. For any questions, project inquiries, or quote requests, please fill out the form below. Our team will review your message and respond as soon as possible.