# Practical Reasoning Interruption Attacks on Reasoning Large Language Models

arXiv: https://arxiv.org/abs/2505.06643 · HTML: https://mlsanity.com/paper/2505.06643/

## Key facts

- Cited by 7 papers in the map (data through 14 Oct 2026).
- Placed in Reasoning for agents, planning and code, one of 17 directions in LLM reasoning.
- Builds on 10 of its 28 references that are in the map.
- First posted on arXiv 10 May 2025.

## Placed in

- LLM reasoning / [Reasoning for agents, planning and code](https://mlsanity.com/lr/reasoning-for-agents-planning-and-code/)
- LLM safety and security / [Safety alignment, refusal and guardrails](https://mlsanity.com/safety/safety-alignment-refusal-and-guardrails/)

## Builds on (most cited first, 10 of 10)

- [Towards Reasoning Era: A Survey of Long Chain-of-Thought for Reasoning Large Language Models](https://mlsanity.com/paper/2503.09567/) (2025)
- [Demystifying Long Chain-of-Thought Reasoning in LLMs](https://mlsanity.com/paper/2502.03373/) (2025)
- [From System 1 to System 2: A Survey of Reasoning Large Language Models](https://mlsanity.com/paper/2502.17419/) (2025)
- [ReConcile: Round-Table Conference Improves Reasoning via Consensus among Diverse LLMs](https://mlsanity.com/paper/2309.13007/) (2023)
- [SafeChain: Safety of Language Models with Long Chain-of-Thought Reasoning Capabilities](https://mlsanity.com/paper/2502.12025/) (2025)
- [A Comprehensive Survey in LLM(-Agent) Full Stack Safety: Data, Training and Deployment](https://mlsanity.com/paper/2504.15585/) (2025)
- [H-CoT: Hijacking the Chain-of-Thought Safety Reasoning Mechanism to Jailbreak Large Reasoning Models, Including OpenAI o1/o3, DeepSeek-R1, and Gemini 2.0 Flash Thinking](https://mlsanity.com/paper/2502.12893/) (2025)
- [The Hidden Risks of Large Reasoning Models: A Safety Assessment of R1](https://mlsanity.com/paper/2502.12659/) (2025)
- [A Mousetrap: Fooling Large Reasoning Models for Jailbreak with Chain of Iterative Chaos](https://mlsanity.com/paper/2502.15806/) (2025)
- [Process or Result? Manipulated Ending Tokens Can Mislead Reasoning LLMs to Ignore the Correct Reasoning Steps](https://mlsanity.com/paper/2503.19326/) (2025)

## Built on by (most cited first, 7 of 7)

- [A Comprehensive Survey on Trustworthiness in Reasoning with Large Language Models](https://mlsanity.com/paper/2509.03871/) (2025)
- [Beyond Correctness: Exposing LLM-generated Logical Flaws in Reasoning via Multi-step Automated Theorem Proving](https://mlsanity.com/paper/2512.23511/) (2025)
- [Strong but Brittle: Simple Attacks Subvert Reasoning-based Safety Guardrails](https://mlsanity.com/paper/2510.11570/) (2025)
- [Rethinking Reasoning: A Survey on Reasoning-based Backdoors in LLMs](https://mlsanity.com/paper/2510.07697/) (2025)
- [RRTL: Red Teaming Reasoning Large Language Models in Tool Learning](https://mlsanity.com/paper/2505.17106/) (2025)
- [RAJ-PGA: Reasoning-Activated Jailbreak and Principle-Guided Alignment Framework for Large Reasoning Models](https://mlsanity.com/paper/2508.12897/) (2025)
- [ReasonBreak: Probing Vulnerabilities in Reasoning-Enabled Vision-Language-Action Models for Autonomous Driving](https://mlsanity.com/paper/2605.29114/) (2026)

## Abstract (arXiv)

Reasoning large language models (RLLMs) have demonstrated outstanding performance across a variety of tasks, yet they also expose numerous security vulnerabilities. Most of these vulnerabilities have centered on the generation of unsafe content. However, recent work has identified a distinct "thinking-stopped" vulnerability in DeepSeek-R1: under adversarial prompts, the model's reasoning process ceases at the system level and produces an empty final answer. Building upon this vulnerability, researchers developed a novel prompt injection attack, termed reasoning interruption attack, and also offered an initial analysis of its root cause. Through extensive experiments, we verify the previous analyses, correct key errors based on three experimental findings, and present a more rigorous explanation of the fundamental causes driving the vulnerability. Moreover, existing attacks typically require over 2,000 tokens, impose significant overhead, reduce practicality, and are easily detected. To overcome these limitations, we propose the first practical reasoning interruption attack. It succeeds with just 109 tokens by exploiting our newly uncovered "reasoning token overflow" (RTO) effect to overwrite the model's final answer, forcing it to return an invalid response. Experimental results demonstrate that our proposed attack is highly effective. Furthermore, we discover that the method for triggering RTO differs between the official DeepSeek-R1 release and common unofficial deployments. As a broadened application of RTO, we also construct a novel jailbreak attack that enables the transfer of unsafe content within the reasoning tokens into final answer, thereby exposing it to the user. Our work carries significant implications for enhancing the security of RLLMs.