FunFuzz: An LLM-Powered Evolutionary Fuzzing Framework

Fuente: arXiv
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Auteurs principaux: Béjar, Mario Rodríguez, Romera-Paredes, B., Hernández-Ramos, Jose L.
Format: Preprint
Publié: 2026
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author Béjar, Mario Rodríguez
Romera-Paredes, B.
Hernández-Ramos, Jose L.
author_facet Béjar, Mario Rodríguez
Romera-Paredes, B.
Hernández-Ramos, Jose L.
contents Modern fuzzers increasingly use Large Language Models (LLMs) to generate structured inputs, but LLM-driven fuzzing is sensitive to prompt initialization and sampling variance, which can reduce exploration efficiency and lead to redundant inputs. We present FunFuzz, a multi-island evolutionary fuzzing framework that runs several isolated searches in parallel and periodically migrates high-value candidates to maintain diversity. FunFuzz derives initial generation prompts from documentation and initializes islands with topic-specific instructions, then continuously adapts prompts using feedback-guided selection. During fuzzing, candidates are prioritized by incremental compiler coverage, while compiler-internal failure signals are used to identify crash-inducing inputs. We evaluate FunFuzz on compiler fuzzing, where inputs are source programs and success is measured by compiler coverage and unique compiler-internal failures. Across repeated 24-hour campaigns on GCC and Clang, FunFuzz achieves higher compiler coverage than previous LLM-driven baselines and discovers more unique failure-triggering inputs.
format Preprint
id arxiv_https___arxiv_org_abs_2605_02789
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle FunFuzz: An LLM-Powered Evolutionary Fuzzing Framework
Béjar, Mario Rodríguez
Romera-Paredes, B.
Hernández-Ramos, Jose L.
Cryptography and Security
Computation and Language
Modern fuzzers increasingly use Large Language Models (LLMs) to generate structured inputs, but LLM-driven fuzzing is sensitive to prompt initialization and sampling variance, which can reduce exploration efficiency and lead to redundant inputs. We present FunFuzz, a multi-island evolutionary fuzzing framework that runs several isolated searches in parallel and periodically migrates high-value candidates to maintain diversity. FunFuzz derives initial generation prompts from documentation and initializes islands with topic-specific instructions, then continuously adapts prompts using feedback-guided selection. During fuzzing, candidates are prioritized by incremental compiler coverage, while compiler-internal failure signals are used to identify crash-inducing inputs. We evaluate FunFuzz on compiler fuzzing, where inputs are source programs and success is measured by compiler coverage and unique compiler-internal failures. Across repeated 24-hour campaigns on GCC and Clang, FunFuzz achieves higher compiler coverage than previous LLM-driven baselines and discovers more unique failure-triggering inputs.
title FunFuzz: An LLM-Powered Evolutionary Fuzzing Framework
topic Cryptography and Security
Computation and Language
url https://arxiv.org/abs/2605.02789