Josselin Feist
Independent Security Researcher at Indépendant
France
Summary
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RockstarJosselin Feist is an independent security researcher based in France with a decade of hands-on experience in binary and smart-contract analysis, fuzzing, and tooling. He rose through technical leadership at Trail of Bits—culminating as Engineering Director—and now runs SecEureka where he focuses on code reviews and bespoke security tool development. His open-source contributions to high-profile projects like Manticore (symbolic execution), Slither (Solidity static analysis) and Ethersplay (EVM disassembly) reflect deep expertise in symbolic reasoning, SMT optimization, and EVM internals. Notably, he has engineered symbolic file handling and test-case generation in Manticore and added nuanced reentrancy checks to Slither, demonstrating an ability to turn research-grade techniques into practical security features. With a PhD-era background in guided symbolic execution and an MSc in Networks and Embedded Systems, he bridges academic rigor and production-ready security engineering.
10 years of coding experience
8 years of employment as a software developer
French, English
Github Skills (25)
solidity10
dis10
python10
evm10
audit10
binarydiff10
code-security10
security10
audit-logging10
code-auditing10
ethereum10
blockchain10
disassembly10
smart-contracts10
symbolic-execution10
Programming languages (16)
Github contributions (5)
crytic/ethersplay
Oct 2017 - Jun 2022
EVM dissassembler
Role in this project:
Back-end Developer
Back-end DeveloperContributions:27 commits, 9 PRs, 18 pushes in 4 years 9 months
Contributions summary:Josselin primarily worked on enhancing an EVM disassembler. They refactored the stack value analysis, incorporating a value set analysis approach and making it parameterizable. Contributions include fixing bugs, improving jump destination analysis, and adding new function signatures. The user demonstrates a deep understanding of the Ethereum Virtual Machine's workings by modifying the disassembler's core logic.
ethereumblockchainevmbinary-ninjasolidity
crytic/slither
Sep 2018 - Jan 2023
Static Analyzer for Solidity and Vyper
Role in this project:Back-end Developer & Security Engineer
Back-end Developer & Security EngineerContributions:31 releases, 95 reviews, 2392 commits in 4 years 5 months
Contributions summary:Josselin's commits primarily focus on enhancing the security and functionality of the Solidity codebase. They addressed vulnerabilities by implementing features such as the `is_reentrant` check and corrected incorrect return statements in assembly code. Furthermore, the user worked on improving the codebase by integrating and applying advanced features such as user-defined types, implementing checks to use the correct operators, and including code comments.
static-analyzerethereumsoliditysmart-contractsanalyzer
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