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Cross-modality Information Check for Detecting Jailbreaking in Multimodal Large Language Models

This is the official repository for "Cross-modality Information Check for Detecting Jailbreaking in Multimodal Large Language Models".

Abstract

We propose Cross-modality Information DEtectoR (CIDER), a plug-and-play jailbreaking detector designed to identify maliciously perturbed image inputs, utilizing the cross-modal similarity between harmful queries and adversarial images. This simple yet effective cross-modality information detector, CIDER, is independent of the target MLLMs and requires less computation cost. Extensive experimental results demonstrate the effectiveness and efficiency of CIDER, as well as its transferability to both white-box and black-box MLLMs.

Findings

1. Adversarial images indeed contain harmful information.
2. Directly utilizing the semantic difference between clean and adversarial images to harmful query is challenging
3. Denoising can reduce harmful information but cannot eliminate
4. Relative shift in the semantic distance before and after denoising can help detect adversarial images.

For detailed explanations, please refer to our paper.

CIDER, a plug-and-play cross-modality information detector

CIDER is implemented on top of the MLLMs to defense optimization-based adversarial jailbreak attacks. Figure in Abstract presents the overview of the CIDER pipeline. Specifically, given a text-image input pair, denoted as <text, img(o)>, CIDER calculates the embeddings of text and image modalities, denoted as $\mathbf{E_{\textit{text}}}$ and $\mathbf{E_{\textit{img(o)}}}$. Then, the built-in denoiser in CIDER will perform 350 denoising iterations on the image(o), calculating the denoised embeddings every 50 iterations, denoted as $\mathcal{E}=\mathbf{E_{\textit{img(d)}}}$. The $\textit{img(o)}$ will be identified as an adversarial example if any $\mathbf{E_{\textit{img(d)}}} \in \mathcal{E}$ satisfy the following condition:

\begin{align}
\langle \mathbf{E_{\textit{text}}}, \mathbf{E_{\textit{img(o)}}} \rangle - \langle \mathbf{E_{\textit{text}}}, \mathbf{E_{\textit{img(d)}}} \rangle >\tau 
\end{align}

where $\langle \cdot \rangle$ represents the cosine similarity and $\tau$ is the predefined threshold. Consequently, CIDER will directly refuse to follow the user's request by responding ``I'm sorry, but I can not assist.'' if the image modality is detected as adversarial. Otherwise, the original image and query will be fed into the MLLM.

Threshold selection

The threshold is selected based on the harmful queries and clean images ensuring that the vast majority of clean images pass the detection. The selection of threshold $\tau$ can be formulated as:

\begin{align}
r=\frac{\sum\mathbb{I}(\langle \mathbf{E^\textit{M}_{\textit{text}}}, \mathbf{E^\textit{C}_{\textit{img(o)}}} \rangle - \langle \mathbf{E^\textit{M}_{\textit{text}}}, \mathbf{E^\textit{C}_{\textit{img(d)}}} \rangle <\tau) }{\# \textit{samples}} 
\end{align}

where $r$ represents the passing rate and $\mathbf{E^\textit{M}_{\textit{text}}}$ , $\mathbf{E^\textit{C}_{\textit{img(o)}}}$ , $\mathbf{E^\textit{C}_{\textit{img(d)}}}$ stand for the embeddings of input query, the input image and denoised image respectively. The threshold $\tau$ is determined by controlling the passing rate $r$. For example, using the $\tau$ when setting $r$ to 95% as the threshold indicates allowing 95% percent of clean images to pass the detection. Regarding balance between TPR and FPR, we selected $\tau$ when $r$ equals 95% as the detection threshold of CIDER.

Performance

Effectiveness

DSR: We first demonstrate the overall DSR that CIDER can achieve and compare it with the baseline method, Jailguard. Table below shows that CIDER achieves a DSR of approximately 80%, while the DSR of Jailguard varies, depending on the target MLLMs. Note that CIDER is independent of the MLLMs, thus the DSR does not vary with the choice of MLLMs. However, Jailguard's detection capability relies heavily on the model's safety alignment, so the DSR also varies. MLLMs with good alignment achieve high DSR (e.g., GPT4V), while poorly aligned MLLMs have relatively low DSR (e.g., InstructBLIP). In other words, Jailguard does not significantly enhance MLLM robustness against adversarial jailbreak attacks, whereas CIDER does. Nonetheless, CIDER achieves a higher DSR than most of the Jailguard results, except Jailguard on GPT4V.

ASR: To evaluate the effectiveness of CIDER, we measure the decline in ASR after applying CIDER. Figure 3 compares the original ASR without defense (red bar), ASR after CIDER (blue bar), and ASR after Jailguard (yellow bar). Note that, Jailguard is solely designed to detect jailbreak input. To ensure a fair comparison, we add an output module following Jailguard's detection. Specifically, if Jailguard detects a jailbreak, it will refuse to respond, similar to CIDER. Otherwise, the MLLM will process the original input.

Across all models, defending with CIDER significantly reduces the ASR, yielding better results than the baseline. This indicates that CIDER effectively enhances the robustness of MLLMs against optimization-based jailbreak attacks. The most notable improvements are seen in LLaVA-v1.5-7B, where ASR drops from 60% to 0%, and in MiniGPT4, from 57% to 9%. For MLLMs with initially low ASRs, such as InstructBLIP and Qwen-VL, ASR is reduced to approximately 2% and 1% respectively. Another notable disadvantage of Jailguard is observed in models like GPT4V, InstructBLIP, and Qwen-VL, which already had strong safety alignment and resistance to adversarial attacks. In these cases, the use of Jailguard resulted in a slight increase in ASR.

We conclude that the threshold determined by CIDER can be effectively applied to different MLLMs due to their shared transformer-based LLM backbones, which generate comparable representations of harmful information. This harmful information, distilled from malicious queries, is embedded into adversarial images using similar optimization-based attacks. As a result, the consistent noise patterns produced by these attacks across different MLLMs can be detected using the same threshold, highlighting the robustness and transferability of CIDER.

Efficiency

Timely inference is crucial for safeguarding MLLMs in real-world applications. The table below shows the time required to process a single input pair and generate up to 300 tokens with different MLLMs, comparing no defense, CIDER, and Jailguard.

CIDER surpasses Jailguard in efficiency, adding only 1.02 seconds per input pair on average, which is relatively acceptable compared to the original inference time. In contrast, Jailguard requires 8-9 times the original processing time. Additionally, CIDER detection is irrelevant to the number of generated tokens in the query answers. Therefore, CIDER does not cause additional overhead when increasing the number of generated tokens, ensuring the stability of CIDER's efficiency.

To further demonstrate CIDER's influence on the original utilities on normal queries, we also evaluate the utility of CIDER protected MLLMs on MM-Vet benchmark, including recognition, OCR, knowledge, language generation, spatial awareness, and math. As shown in Figure 4, employing CIDER leads to an approximate 30% overall performance decline on normal tasks. Specifically, CIDER mostly affects the MLLM's recognition, knowledge, and language generation capabilities, while it has minimal impact on OCR, spatial awareness, and math skills. We hypothesize that CIDER's stringent decision-making process, which outright rejects tasks once an image is identified as adversarial, hampers the model's overall performance. An ablation study is also included in the paper.

Getting Started

Installation

1. Prepare the code and the environment

You may need to install git-lfs first if it has't been installed before.

Git clone our repository, creating a python environment and activate it via the following command

git clone https://github.com/PandragonXIII/CIDER.git
cd CIDER
conda create -n CIDER python=3.10
pip install -r newrequirements.txt
conda activate CIDER

2. Prepare the pretrained VLM weights CIDER rely on existing VLMs to calculate embeddings and generate answers. LLaVA-1.5-7b is required.

Download HarmBench to evaluate the harmfulness of generated answers.

Diffusion based denoiser weight: Link and place it at code/models/diffusion_denoiser/imagenet/256x256_diffusion_uncond.pt.

To generate responses with more Models, download:

• Qwen-VL-Chat
• instructblip-vicuna-7b
• MiniGPT-4(vicuna):
  1. Download the corresponding LLM weights from the following huggingface space via clone the repository using git-lfs. Then set the path in code/models/minigpt4/configs/models/minigpt4_vicuna0.yaml
  2. Download the pretrained model checkpoints. Then set the path in code/models/minigpt4/configs/models/minigpt4_vicuna0.yaml.

After downloading these models, remember to set the paths in settings/settings.yaml.

for detailed information, see also :

• Diffusion Denoised Smoothing
• guided-diffusion is the This is the codebase for Diffusion Denoised Smoothing.
• offical repository of MiniGPT-4
• offical repository of HarmBench
• Qwen-VL-Chat on huggingface
• LLaVA on huggingface

Preparing data

The image inputs should be placed under data/img/your_dataset_name/, and texts stored in csv format in data/text/text_file_name.csv. Note that clean images should be named with prefix "clean_" and adversarial images with prefix "prompt_constrained_" (This is necessary only when calculating confusion matrix). Also, the csv file prefer a Harmbench-like format, and our test set as well as validation set are taken from 'standard' behaviors from Harmbench.

Select a threshold

The threshold is selected utilizing a bunch of clean images. Through validation set it is possible to see the effect of hyperparameter $r$ which stands for the passing rate of clean images. Take data/img/clean and data/img/valset, for example. Simply running

python3 ./code/threshold_selection.py

would generate a directory output/valset_analysis, in which the tpr-fpr plot reflects how $r$ influences CIDER's detect ability. The left-upper point indicates better overall performance. Exact $\tau$ values will be printed in the terminal.

Evaluation

With a specified threshold, we can evaluate it under test set or other benchmarks through following command:

python3 ./auto_evaluate.py

You may have to change the settings in auto_evaluate.py in advance. Check code/main.py for usages of arguments. Logs, generated responses and evaluation results are stored under output/{group_dir}/{name} by default.

There is another way to evaluate directly with commandline, for example:

python3 ./code/main.py --text_file data/text/valset.csv --img data/img/valset --outdir output/valset_output &

required arguments:

• text_file: path to a csv containing harmful queries with out headings, and each query takes up one line .
• img: path to the folder containing input images.
• outdir: directory to place the output files. optional arguments:
• threshold: The threshold $\tau$ of Delta cosine similarity distinguishing adversarial images.
• model: The VLM that generate responses to the query-image pairs, could be one of "llava", "blip","minigpt4","qwen","gpt4".
• cuda: GPU id.
• pair_mode: relation between imgs and queries, should be "combine" or "injection". combine mode will iterate through all images and queries, forming |img|*|query| number of img-query pairs; injection requires |img|==|query| and each image corresponding to one query.
• multirun: run evaluation multiple times to calculate average score.
• tempdir: temporary directory path to store intermediate files (like denoised images).
• denoiser: should be "diffusion" or "dncnn". Reminder: DnCNN do not support multi-stage denoising.
• no_eval: A flag argument. It will skip Harmbench evaluation phase once added.
• no_defence: A flag argument. It will skip CIDER defence phase once added.

Acknowledgements

• We thank all reviewers for their constructive comments.
• This work is supported by the Shanghai Engineering Research Center of Intelligent Vision and Imaging and the Open Research Fund of The State Key Laboratory of Blockchain and Data Security, Zhejiang University.
• Thanks for all contributors of guided-diffusion,HarmBench,LLaVA,MiniGPT,Qianwen and all other repositories.

Citation

If you find CIDER useful for your research and applications, please cite using the Bibtex:

@inproceedings{xu2024cross,
  title={Cross-modality Information Check for Detecting Jailbreaking in Multimodal Large Language Models},
  author={Xu, Yue and Qi, Xiuyuan and Qin, Zhan and Wang, Wenjie},
  booktitle={Findings of the Association for Computational Linguistics: EMNLP 2024},
  pages={13715--13726},
  year={2024}
}