Autonomous Penetration Testing: Solving Capture-the-Flag Challenges with LLMs

This study evaluates the ability of GPT-4o to autonomously solve beginner-level offensive security tasks by connecting the model to OverTheWire's Bandit capture-the-flag game. Of the 25 levels that were technically compatible with a single-command SSH framework, GPT-4o solved 18 unaided and another two after minimal prompt hints for an overall 80% success rate. The model excelled at single-step challenges that involved Linux filesystem navigation, data extraction or decoding, and straightforward networking. The approach often produced the correct command in one shot and at a human-surpassing speed. Failures involved multi-command scenarios that required persistent working directories, complex network reconnaissance, daemon creation, or interaction with non-standard shells. These limitations highlight current architectural deficiencies rather than a lack of general exploit knowledge. The results demonstrate that large language models (LLMs) can automate a substantial portion of novice penetration-testing workflow, potentially lowering the expertise barrier for attackers and offering productivity gains for defenders who use LLMs as rapid reconnaissance aides. Further, the unsolved tasks reveal specific areas where secure-by-design environments might frustrate simple LLM-driven attacks, informing future hardening strategies. Beyond offensive cybersecurity applications, results suggest the potential to integrate LLMs into cybersecurity education as practice aids.