Custom GPT and Agent Security
Agents do work. That means they have privileges. That means compromise has consequences. Treat agents like service accounts that can be reasoned into bad decisions.
- Vendor
- Custom GPT / agent architectures
- Product
- OpenAI GPTs, custom agentic systems
- Guide covers
- Central risk, specific risks, recommended controls, and your Posture Check checkpoint
What it is
Custom GPTs (OpenAI's brand) and custom agents (general term) are LLM-based systems with tool access: the ability to call APIs, execute code, send emails, modify systems. They differ from chatbots by taking actions instead of only producing text. Compromise of an agent through prompt injection has direct operational consequences.
The central risk
Excessive agency (LLM06). An agent with broad tool access plus prompt-injection vulnerability becomes a compromised privileged account. Mitigation requires least-privilege tool scope, action confirmation gates for high-impact operations, and audit logging.
Specific risks in OpenAI GPTs, custom agentic systems
Prompt injection bypassing intended task constraints (LLM01)
Excessive agency via over-broad tool permissions (LLM06)
Improper output handling causing downstream injection (LLM05)
Unbounded consumption from runaway recursive agent loops (LLM10)
Plug-in supply-chain risk for OpenAI custom GPTs (LLM03)
Recommended controls
Principle of least privilege for tool access tokens
Human-in-the-loop confirmation for high-impact actions
Action audit logging
Recursion and resource limits
Adversarial testing of prompt-to-action paths
Plug-in review for custom GPTs
Score yourself before you roll out OpenAI GPTs, custom agentic systems.
The AI Posture Check is a free five-question adaptive self-assessment that maps your gaps to specific OWASP LLM Top 10 risks for OpenAI GPTs, custom agentic systems.
Runtime controls, including rate limiting and isolation, feed your AI Posture Check stage.
Take the AI Posture CheckGet a Standard Audit on your OpenAI GPTs, custom agentic systems deployment.
A senior CWS engineer reviews your specific deployment, runs adversarial tests, and produces a remediation roadmap.