Corrupt Plans, Clean Traces: Evading Chain-of-Thought Monitoring with Plan Injection
By Keertana Chidambaram, Andrew Ilyas, Vasilis Syrgkanis
The paper demonstrates a plan-injection attack in which language models follow corrupted reasoning while producing plausible, independently worded chain-of-thought traces that hide the source of the error. Follow rates reach 93.0% and 98.9% on programming and Bio-Math tasks across 8B and 671B actors, and monitors detect no more than roughly 75% of attacks, sometimes becoming less effective when shown the injected plan.