Linear probes for prompt injection often detect conversation position, not attacks

By training with matched negatives—clean twins and look-alikes—the authors cut false alarms from 41–80% to 4–27% on injection-free conversations across six models.

Academic
Kaan Kale · Sriram Vishwanath

Georgia Institute of Technology

Research Digest··3 min read
Linear probes on hidden states are used as fast filters for indirect prompt injection in LLM agents.

The authors trained linear probes on hidden states of six open text models from four families, using the BTPool-1 dataset of multi-turn agent tasks with injected attacks.

Why this paper

From Georgia Institute of Technology

In one line

Prompt-injection probes trained on standard examples learn conversation position and text length, not injection content; adding matched negatives cuts false alarms while catching most attacks.

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