Cross-Domain Resource Abuse in MCP Tool Invocations (mitigated by AEGIS)

Technical Analysis

The underlying weakness is that MCP tool schemas across text, image, video, and location modalities allow wide parameter ranges without consistent bounds, so an agent (malicious or simply misconfigured) can issue requests with disproportionately large parameters (e.g., oversized search radius, excessive video duration) that overload backend systems. The entry point is the tool invocation layer of MCP, where heterogeneous request schemas make uniform validation difficult. An attacker gains denial-of-service or quality-of-service degradation rather than data access or code execution, and the issue crosses tool/domain boundaries because a single agent can chain or repeat abusive calls across different modality-specific tools. AEGIS addresses this by using LLM-based normalization of diverse tool calls into a unified representation, then enforcing fine-grained policies via Open Policy Agent integrated with the ContextForge AI Gateway.

Affected Systems

ContextForge AI Gateway, Open Policy Agent; protocols: MCP

Detection Signatures

• Abnormally large numeric parameters in tool calls (e.g., search_radius, duration, resolution) far exceeding typical usage baselines
• Repeated high-cost tool invocations from a single agent/session in a short time window
• Requests spanning multiple modalities (text/image/video/location) with parameters near or at schema maximums
• Lack of upper-bound validation in MCP tool parameter schemas
• Spikes in backend latency or resource utilization correlated with specific agent/tool invocation patterns

Remediation Steps

1. 1

   Enforce parameter bounds

   Define and enforce strict min/max limits on resource-affecting parameters (radius, duration, resolution, count) for every MCP tool schema.

2. 2

   Deploy policy enforcement layer

   Integrate a policy engine (e.g., Open Policy Agent as used by AEGIS) in front of MCP tool execution to normalize and validate cross-modal requests before they reach backend systems.

3. 3

   Rate limit and quota agents

   Apply per-agent/per-session rate limiting and resource quotas to prevent repeated high-cost tool calls from degrading shared infrastructure.

4. 4

   Monitor and alert on anomalous requests

   Implement telemetry that flags tool invocations with parameters near schema maximums or unusual multimodal request patterns for review.

5. 5

   Adopt unified request normalization

   Use a normalization layer to map heterogeneous tool schemas into a consistent representation so security policies can be applied generically across modalities.