When Context Bites: Detecting RAG Poisoning via Document-Level Attention Collapse

D-SCAN is an analysis framework for detecting document poisoning attacks in RAG (Retrieval-Augmented Generation) systems. It collects LLM internal states during generation (token probabilities and attention weights), extracts multi-dimensional features, and trains classifiers to distinguish between clean and poisoned retrieved documents.

1. Installation & Requirements

Prerequisites

• Python >= 3.9
• CUDA-compatible GPU (>= 24GB VRAM recommended for 8B-parameter model inference)

Model Preparation

This project uses Llama-3.1-8B-Instruct by default. Download the model to a local path and update the MODEL_ID variable in collect_inner_state.py:

MODEL_ID = "/your/path/to/Llama-3.1-8B-Instruct"

2. Quick Start

The full workflow consists of three steps: Collect Internal States → Compute Features → Train Classifier. The question and related retrieved documents are provided in https://huggingface.co/datasets/An998/D-SCAN.

Step 1: Collect Model Internal States

# Update configuration parameters in collect_inner_state.py, then run
python collect_inner_state.py

Step 2: Compute Feature Metrics

# Analyze both attack and clean data, compute all features, and save results
python compute_feature.py \
    --attack_dir ./saved_reppl_weights_serial_query1_attack2_2wiki \
    --clean_dir ./saved_reppl_weights_serial_query1_pure1_5_2wiki \
    --output_dir ./analysis_results/2wiki_all \
    --max_attack_samples 3000 \
    --max_clean_samples 3000

Step 3: Train Classifier and Evaluate

Open fit_D-SCAN.ipynb and execute cells sequentially to:

1. Load the feature data generated in Step 2
2. Train Logistic Regression / Random Forest classifiers (5-Fold CV)
3. Evaluate transfer performance on the test set

3. Pipeline Details

3.1 Data Collection (collect_inner_state.py)

For each question-document input, the LLM performs multi-sample generation (default: 10 samples, temperature=1.0) and collects the following internal states:

Key Configuration Parameters

MODEL_ID = "/path/to/model"     # Model path
NUM_SAMPLES = 10                # Number of samples per question
MAX_NEW_TOKENS = 50             # Maximum generated tokens
TEMPERATURE = 1.0               # Sampling temperature
data_type = 'pure1_5'           # Data type: 'pure1_5' (clean) or 'attack2' (attack)
dataset_name = 'hotpotqa'       # Dataset: 'hotpotqa', '2wiki', 'musique'

Outputs are saved as data_{batch_id}_reppl.pt files and results_stats_*.jsonl statistics files.

3.2 Feature Computation (compute_feature.py)

Extracts 10 categories with 100+ dimensional features from the collected internal states. The classifier uses these features to determine whether poisoned documents exist among the retrieved documents for a given query.

Metric Overview

Detailed Metric Descriptions

1. PerplexityMetrics (Generation Probability Statistics)

Computed from outer_ppl_probs (probability of each generated token):

• ppl_mean_prob: Mean probability across all generated tokens
• ppl_std_prob: Probability standard deviation
• ppl_min_prob: Minimum probability (extreme uncertainty)
• ppl_low_prob_ratio: Ratio of low-probability tokens (<0.1)
• ppl_cross_sample_var: Variance of mean probabilities across samples
• ppl_coef_variation: Coefficient of variation (CV = std/mean)
• ppl_skewness: Probability distribution skewness
• ppl_kurtosis: Probability distribution kurtosis

2. AttentionEntropyMetrics (Attention Entropy)

Computed from inner_ppl_matrix (attention weights at each step):

• attn_entropy_mean/std/max: Mean, standard deviation, and maximum of attention distribution entropy
• attn_entropy_cv: Coefficient of variation of attention entropy

3. AttentionConcentrationMetrics (Attention Concentration)

• attn_top5/10/20_ratio_mean/std: Attention share captured by the Top-K% tokens
• attn_gini_mean/std: Gini coefficient of the attention distribution (inequality measure)

4. DocumentAttentionDensityMetrics (Document Attention Density)

• doc_attn_dens_std/range/max/min: Std, range, max, and min of attention density across documents
• doc_attn_dens_entropy: Entropy of document attention density distribution
• doc_attn_dens_temporal_var_mean: Mean temporal variance of document attention density

5. SampleConsistencyMetrics (Multi-Sample Consistency)

• sample_attn_consistency/std: Cross-sample cosine similarity of token-level attention
• sample_doc_consistency: Cross-sample cosine similarity of document-level attention
• sample_doc_js_divergence: Cross-sample JS divergence of document-level attention

6. AttentionDynamicsMetrics (Attention Dynamics)

• attn_doc_switch_mean/max: Dominant document switch count
• attn_entropy_change_mean/std: Step-wise attention entropy change

7. TokenLevelAttentionMetrics (Token-Level Attention Fluctuation)

• tla_std_mean/std/max/median/p90/p99/high_ratio/cv: Statistics of per-token attention std across generation steps
• tla_ent_mean/std/max/median/p90/p99/high_ratio/cv: Statistics of per-token attention entropy across generation steps

8. AnswerProbabilityMetrics (Answer Probability Deep Statistics)

• aprob_p10/p25/p50/p75/p90/iqr: Probability quantiles
• aprob_high_ratio_05/08: Ratio of high-probability tokens
• aprob_low_ratio_01/001: Ratio of low-probability tokens
• aprob_log_mean/std/min: Log-probability statistics
• aprob_ppl_mean/std/max: Sequence-level perplexity
• aprob_geometric_mean: Geometric mean of probabilities
• aprob_distribution_entropy: Information entropy of the probability histogram

9. ProbabilityDynamicsMetrics (Probability Dynamics)

• pdyn_diff_mean/abs_diff_mean/abs_diff_std/abs_diff_max: Probability difference statistics
• pdyn_max_drop/max_jump: Maximum single-step drop/jump
• pdyn_volatility_mean/std: Volatility
• pdyn_trend_slope_mean/std: Linear trend slope
• pdyn_autocorr_mean/std: Autocorrelation coefficient
• pdyn_spike_ratio_01/03: Spike (mutation point) ratio

10. CrossSampleProbabilityConsistencyMetrics (Cross-Sample Probability Consistency)

• cspc_mean_prob_std/cv/range: Consistency of mean probabilities across samples
• cspc_ppl_std/cv/range: Consistency of perplexity across samples
• cspc_min_prob_std/range: Consistency of minimum probabilities
• cspc_seq_cosine_mean/std: Cross-sample cosine similarity of probability sequences
• cspc_seq_pearson_mean: Cross-sample Pearson correlation of probability sequences
• cspc_seq_mse_mean: Cross-sample MSE of probability sequences
• cspc_divergence_index: Inter-sample divergence index

compute_feature.py Command-Line Arguments

python compute_feature.py \
    --attack_dir <attack_data_directory> \
    --clean_dir <clean_data_directory> \
    --output_dir <output_directory> \
    --max_attack_samples 3000 \
    --max_clean_samples 3000 \
    --min_correct_count 0 \
    --min_attack_target_count 0 \
    --num_use_samples 10 \
    --model_path /path/to/model    # Optional: load tokenizer for accuracy calculation

Output Files

3.3 Classifier Training (fit_D-SCAN.ipynb)

Notebook workflow:

1. Load Data: Read full_analysis_results.json output from compute_feature.py
2. Feature Selection: Use all features or filter by category (e.g., attention-only features)
3. Train Classifiers:
   • Logistic Regression (L2 regularization): Linear classifier, suitable for fewer features
   • Random Forest (100 trees, max_depth=5): Non-linear classifier, captures feature interactions
4. 5-Fold Cross-Validation: Reports AUC, Accuracy, Precision, Recall, F1
5. Feature Importance Analysis: Outputs Top-10 important features
6. Test Set Evaluation: Uses training scaler and classifier to evaluate transfer performance on an independent test set
7. Visualization: ROC curves, feature importance bar charts, Train vs Test comparison

Feature Selection for Classifiers

The use_features variable in the notebook provides flexible control over the feature subset used by classifiers:

# Use all features
use_features = [f for f in feature_names if f not in exclude_cols]

# Use only attention-related features
use_features = [f for f in use_features if 'attn' in f]

# Combine by metric category (example)
use_features = [f for f in feature_names if f.startswith(('ppl_', 'doc_', 'sample_'))]

Per-category classifier performance is also printed during compute_feature.py execution:

Citation

If you find our work useful, please consider citing our paper:

Paper: When Context Bites: Detecting RAG Poisoning via Document-Level Attention Collapse

@inproceedings{dscan,
author = {Ren, Yingtao and Zhao, Ziyi and Fu, Yiwei and Luo, Xiao and Chang, Yu-Cheng and Lin, Chin-Teng},
title = {When Context Bites: Detecting RAG Poisoning via Document-Level Attention Collapse},
year = {2026},
isbn = {9798400725999},
publisher = {Association for Computing Machinery},
address = {New York, NY, USA},
url = {https://doi.org/10.1145/3805712.3809904},
doi = {10.1145/3805712.3809904},
booktitle = {Proceedings of the 49th International ACM SIGIR Conference on Research and Development in Information Retrieval},
pages = {4080–4086},
numpages = {7},
keywords = {retrieval-augmented generation, information security, question answering system},
location = {Australia},
series = {SIGIR '26}
}