Do Agents Dream of Root Shells? Partial-Credit Evaluation of LLM Agents in Capture The Flag Challenges

2026-04-21

AI Summary

Current large language model (LLM) agents lack systematic evaluation in real-world cybersecurity tasks requiring multi-step reasoning and tool usage. To address this gap, this work proposes DeepRed—the first CTF agent evaluation framework that supports partial scoring. DeepRed enables fine-grained quantification of complex offensive and defensive behaviors through isolated virtual target machines, integrated terminal tools, optional web search, execution trace logging, challenge-embedded checkpoints, and automated log analysis. Evaluated on ten VM-based CTF challenges across ten leading commercial LLMs, the best-performing model completed only 35% of checkpoints on average, revealing significant limitations in current agents’ capabilities for discovering unconventional vulnerabilities and adapting over extended reasoning chains.

Technology Category

Cognitive Modeling & Cognitive Systems: Agent ArchitecturesMultiagent Systems: Adversarial AgentsMachine Learning: Large Multimodal Models (LMMs)

Application Category

Search and Retrieval-Augmented AI: Web evaluation methodologies and metricsSemantics and Knowledge: Data modeling to support human-machine intelligence, including LLMs agents, intelligent system behavior, explanations, and user-friendly interactionsEconomics, Online Markets and Human Computation: Cost models of using LLMs in production systems

Abstract

Large Language Model (LLM) agents are increasingly proposed for autonomous cybersecurity tasks, but their capabilities in realistic offensive settings remain poorly understood. We present DeepRed, an open-source benchmark for evaluating LLM-based agents on realistic Capture The Flag (CTF) challenges in isolated virtualized environments. DeepRed places an agent in a Kali attacker environment with terminal tools and optional web search, connected over a private network to a target challenge, and records full execution traces for analysis. To move beyond binary solved/unsolved outcomes, we introduce a partial-credit scoring method based on challenge-specific checkpoints derived from public writeups, together with an automated summarise-then-judge labelling pipeline for assigning checkpoint completion from logs. Using DeepRed, we benchmark ten commercially accessible LLMs on ten VM-based CTF challenges spanning different challenge categories. The results indicate that current agents remain limited: the best model achieves only 35% average checkpoint completion, performing strongest on common challenge types and weakest on tasks requiring non-standard discovery and longer-horizon adaptation.

Problem

• LLM agents
• cybersecurity
• Capture The Flag
• evaluation benchmark
• partial-credit scoring

Innovation

• partial-credit evaluation
• LLM agents
• Capture The Flag
• automated scoring
• cybersecurity benchmarking