RoguePrompt: Dual-Layer Ciphering for Self-Reconstruction to Circumvent LLM Moderation

Abstract: Content moderation pipelines for modern LLMs combine static filters, dedicated moderation services, and alignment tuned base models, yet real world deployments still exhibit dangerous failure modes. This paper presents RoguePrompt, an automated jailbreak attack that converts a disallowed user query into a self reconstructing prompt which passes provider moderation while preserving the original harmful intent. RoguePrompt partitions the instruction across two lexical streams, applies nested classical ciphers, and wraps the result in natural language directives that cause the target model to decode and execute the hidden payload. Our attack assumes only black box access to the model and to the associated moderation endpoint. We instantiate RoguePrompt against GPT 4o and evaluate it on 2 448 prompts that a production moderation system previously marked as strongly rejected. Under an evaluation protocol that separates three security relevant outcomes bypass, reconstruction, and execution the attack attains 84.7 percent bypass, 80.2 percent reconstruction, and 71.5 percent full execution, substantially outperforming five automated jailbreak baselines. We further analyze the behavior of several automated and human aligned evaluators and show that dual layer lexical transformations remain effective even when detectors rely on semantic similarity or learned safety rubrics. Our results highlight systematic blind spots in current moderation practice and suggest that robust deployment will require joint reasoning about user intent, decoding workflows, and model side computation rather than surface level toxicity alone.