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| 1 | +# Erratum / Corrigendum |
| 2 | + |
| 3 | +**Paper:** *Can Model Internals Detect MCP Tool Poisoning That Text Analysis Cannot?* |
| 4 | +**DOI:** [10.5281/zenodo.19990741](https://doi.org/10.5281/zenodo.19990741) |
| 5 | +**Date:** 2026-06-18 |
| 6 | + |
| 7 | +This erratum corrects errors in the preliminary study and clarifies how its numbers |
| 8 | +relate to the shipped IntentProbe product. The paper remains a preliminary GPT-2 |
| 9 | +proof-of-concept. The current, defensible evidence is the Qwen2.5-0.5B cross-source |
| 10 | +generalization results in this repository (`research/_results_published/`). |
| 11 | + |
| 12 | +## Corrections |
| 13 | + |
| 14 | +1. **The matched-pair headline F1 (97.5% / 98.5%) was inflated by pair leakage.** The |
| 15 | + original matched-pair evaluation did not fully separate the two halves of each |
| 16 | + minimal pair across train/test. Under leak-free GroupKFold by pair, the |
| 17 | + within-distribution result is a **tie** with a TF-IDF text baseline (~0.79 vs ~0.82 |
| 18 | + AUROC), not a decisive probe win. The "structurally blind to same-vocabulary |
| 19 | + attacks" framing is withdrawn. |
| 20 | + |
| 21 | +2. **The same-words result was confounded by length/framing at low layers.** A |
| 22 | + length-only baseline is at chance, but controlling for length and framing does not |
| 23 | + by itself establish the probe reads "intent." The surviving claim is generalization |
| 24 | + to novel-source / novel-vocabulary attacks, not same-vocabulary detection. |
| 25 | + |
| 26 | +3. **The statistics were underpowered and did not respect pairing** (n ≈ 100; a |
| 27 | + permutation test that did not respect the pair structure). The corrected repository |
| 28 | + results use bootstrap confidence intervals and grouped/paired resampling. |
| 29 | + |
| 30 | +4. **"485 MCPTox descriptions" is a self-selected subset.** The MCPTox benchmark |
| 31 | + contains 1,312 poisoned descriptions; the paper used a 485-item subset. It should |
| 32 | + read "a 485-item subset of MCPTox." |
| 33 | + |
| 34 | +5. **"2,059 SAE neurons" should read 1,758 SAE features** (Safe-SAIL). |
| 35 | + |
| 36 | +6. **The 96.5% / 96.6% / 100% figures are GPT-2 research-probe numbers, not |
| 37 | + shipped-product performance.** The shipped product uses Qwen2.5-0.5B. Its current |
| 38 | + evidence is recall on a held-out real-attack source (HackAPrompt: 90.3% at a 5% |
| 39 | + clean false-positive rate, vs a same-data TF-IDF baseline's 52.8%) and curated |
| 40 | + cross-source AUROC (0.984 vs 0.914, CI-backed). These supersede the paper's headline |
| 41 | + numbers for any product claim. |
| 42 | + |
| 43 | +## What stands |
| 44 | + |
| 45 | +The core hypothesis — that a linear probe on a frozen model's mid-layer activations |
| 46 | +generalizes to attacks worded in ways a text classifier never saw, better than a |
| 47 | +same-data text classifier — is supported by the corrected, CI-backed cross-source |
| 48 | +results in the repository. The contribution is generalization in a specific deployment |
| 49 | +shape; it is not a new state of the art and not first-of-technique (PIShield, |
| 50 | +TaskTracker, RouteGuard, MindGuard, and frontier-lab production probes predate or |
| 51 | +parallel it). |
| 52 | + |
| 53 | +All corrected benchmarks and scripts: <https://github.com/mcpware/IntentProbe> (`research/`). |
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