AI Data Theft: Hidden Prompts in Downscaled Images
- Researchers have uncovered a complex attack that exploits a vulnerability in how AI systems process images.
- Modern AI systems frequently enough rely on image processing to understand user input.
- Specifically, the researchers at Trail of Bits, Kikimora Morozova and Suha Sabi Hussain, demonstrated that carefully crafted images can contain instructions invisible to the human eye. These instructions...
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(Last Updated: October 26, 2023)
Researchers have uncovered a complex attack that exploits a vulnerability in how AI systems process images. This method allows attackers to steal user data by embedding hidden instructions within images, which are then executed by large language models (LLMs). The attack leverages the image downscaling process common in many AI applications, making it particularly insidious and arduous to detect.
Modern AI systems frequently enough rely on image processing to understand user input. To optimize performance and reduce computational costs,uploaded images are frequently downscaled – their resolution is reduced.This process, while efficient, introduces a critical vulnerability. The attack hinges on the fact that certain image resampling algorithms can reveal hidden patterns embedded within the original, high-resolution image when it’s downscaled.
Specifically, the researchers at blank” rel=”nofollow noopener”>2020 USENIX paper from TU Braunschweig, which initially explored the potential for image-scaling attacks in machine learning. The Trail of bits research successfully weaponizes this theory into a practical attack.
How the Attack Works: A Step-by-Step Breakdown
- Image Crafting: The attacker creates a high-resolution image containing a hidden message. This message is embedded using subtle color variations or patterns that are imperceptible to the human eye.
- Image Upload: The user uploads the malicious image to an AI system.
- Downscaling: The AI system automatically downscales the image for efficiency.
- Hidden Message Reveal: The downscaling process, particularly with bicubic interpolation (as demonstrated by the researchers), reveals the hidden message as readable text. In the Trail of Bits example, dark areas of the image transform to reveal black text on a red background.
- Prompt Injection: The AI model interprets the revealed text as part of the user’s instructions, effectively injecting malicious commands into the system.
- Data Exfiltration/Unauthorized Action: The AI model executes the injected commands, possibly leading to data leakage, unauthorized access, or other harmful actions.

Source: Zscaler
Real-World Implications and Demonstrated Attacks
The researchers successfully demonstrated the attack against several AI systems, highlighting the real-world threat.
