Blog October 9, 2025

What is an LLM Firewall?

Unlike a traditional firewall that polices IP packets, an LLM firewall inspects natural language—the prompts users send and the responses models return. It organizes protection into four signal groups—User, Safety, Security, and LLM—to shield enterprises from AI security risks.

What is an LLM Firewall?

Traditionally, a firewall processes IP packets, policing network traffic based on protocols, IP source/destination, ports and other criteria such as payload type, etc.

In contrast, an LLM firewall inspects, analyzes, and polices traffic based on natural language – the users’ prompts and LLM responses. An LLM firewall protects enterprises and users from adverse effects and AI security risks associated with using large language models.

Cranium acts as an LLM firewall, segmenting functionality and utility into four groups:

1. User

The first group of “Signals” used to safeguard and secure LLM traffic is based on the LLM user. It consists of user sentiment, intention and named entities, which are specific real-world things like names of people, places, companies, or dates that are recognized and extracted from text. This allows Cranium to determine the user’s objective and the subject of that objective. For example, a user being frustrated with using a chatbot for resolving a technical issue might be of negative sentiment, intended to seek knowledge and clarification for a specific subject. This allows for user behavior monitoring and the establishment of safe baselines for a given LLM use case.

2. Safety

Safety covers Signals that deal with the exposure and disclosure of Secrets, PII, PHI, PCI, Illegality, Toxicity (hate speech, racism, vulgarity, etc.) and user-defined blocklists. Safety signals such as PII/PHI/PCI are in addition relevant and required for AI risk management and compliance.

3. Security

Analyzes user prompts against known LLM attack vectors such as prompt injection, jailbreaking or prompt leaking. The usage of source code and safety of source code is also part of the AI security signal group whether a user is asking for source code and/or the LLM is providing source code. The ability to identify code, coding language and safety will become increasingly important as we move into the age of agentic AI.

4. LLM

While some of the previous signals are also applied to the LLM response, LLM as a signal group deals with qualitative measures of the LLM response, such as context adherence, chunk utilization, or specificity. Such signals not only help determine response quality but also allow for AI threat detection of manipulated responses.

Advanced LLM firewall features add query and context relevance, data-loss protection as well as employee LLM proxy functionalities.

See Cranium in Action

See how an LLM firewall inspects every prompt and response in real time — schedule a personalized demo: cranium.ai/get-a-demo/