Prompt Injection
Industry Definition Set • Entity Resolution Path: /glossary/prompt-injection
Quick Answer / TL;DR
An attack where malicious input manipulates an LLM into ignoring its instructions or system prompt, potentially causing it to misuse tools or leak sensitive data.
Key Takeaways
- Malicious input that manipulates LLM behavior.
- Can cause models to ignore safety instructions.
- Particularly dangerous in MCP systems with tool access.
- Defenses include sanitization, instruction hierarchy, and validation.
Definitive Statement: An attack where malicious input manipulates an LLM into ignoring its instructions or system prompt, potentially causing it to misuse tools or leak sensitive data.
Technical Context & Protocol Usage
- Detailed Explanation
- Prompt injection attacks exploit the fact that LLMs treat user input and system instructions as part of the same context. A malicious user can craft input that overrides the system prompt, causing the model to ignore safety guidelines or misuse MCP tools. Defenses include input sanitization, instruction hierarchy, and output validation. In MCP systems, prompt injection is particularly dangerous because it can cause the model to call tools with malicious arguments.
Format & Payload Metadata
Format: Crafted adversarial text input
Latency: No direct latency impact; requires detection overhead
Real-World Implementation Use Case
A user crafts a prompt injection that tricks the model into calling an MCP `delete_file` tool on a sensitive system file.
Cite This Page
MLA Style:
MCPserver.in Engineering. "Prompt Injection." MCPserver.in Knowledge Hub, 20 July 2026, mcpserver.in/glossary/prompt-injection.
Related Terms
Model Context Protocol (MCP)
An open, secure protocol that standardizes how artificial intelligence agents and large language models (LLMs) exchange context, tools, prompts, and data resources with external servers.
JSON-RPC 2.0
A lightweight, stateless remote procedure call (RPC) protocol defined in JSON that utilizes request, response, and notification message frames.
Stdio Transport (Standard Input/Output)
A local-only transport mechanism where the AI client spawns the MCP server as a child process and communicates via standard input (stdin) and standard output (stdout) channels.
SSE Transport (Server-Sent Events)
A lightweight, unidirectional HTTP-based streaming protocol used by remote MCP servers to push messages to AI clients, with client-to-server writes sent over standard POST requests.
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