Soft Instruction De-escalation Defense
Authors: name: Nils Philipp Walter; name: Chawin Sitawarin; name: Jamie Hayes; name: David Stutz; name: Ilia Shumailov
Published: 2025-10-24 00:04:07

Abstract: Large Language Models (LLMs) are increasingly deployed in agentic systems
that interact with an external environment; this makes them susceptible to
prompt injections when dealing with untrusted data. To overcome this
limitation, we propose SIC (Soft Instruction Control)-a simple yet effective
iterative prompt sanitization loop designed for tool-augmented LLM agents. Our
method repeatedly inspects incoming data for instructions that could compromise
agent behavior. If such content is found, the malicious content is rewritten,
masked, or removed, and the result is re-evaluated. The process continues until
the input is clean or a maximum iteration limit is reached; if imperative
instruction-like content remains, the agent halts to ensure security. By
allowing multiple passes, our approach acknowledges that individual rewrites
may fail but enables the system to catch and correct missed injections in later
steps. Although immediately useful, worst-case analysis shows that SIC is not
infallible; strong adversary can still get a 15% ASR by embedding
non-imperative workflows. This nonetheless raises the bar.