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10/14/2025

When AI Becomes the Attack Surface

 
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It’s 2025 and AI agents are now critical to many business processes. This is creating a massive shift in security needs. AI is now an attack surface, not just a tool. Traditional defenses fail against attacks on the model's reasoning layer. Layered defenses must now include reasoning-layer protection to detect malicious intent pre-action.
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​By, Bill Miller


AI agents have moved from novelty to mission-critical deployment. As organizations embed assistants, copilots, and autonomous agents into their infrastructure, the security stakes have shifted: AI is no longer just a tool to protect - it is itself an attack surface. The classic perimeter-only defense model is breaking down under new assaults that penetrate the model’s reasoning layer. Recent revelations such as the Gemini Trifecta, new G7 cybersecurity policy statements, and vendor moves like CrowdStrike’s AIDR confirm this shift. Layered defenses must now include reasoning-layer instrumented protection to catch malicious intent before it translates into action.

From Chat to Agents → From Advice to Action (and New Failure Modes)
Agentic systems orchestrate tools such as search, APIs, databases, and shell execution under the control of LLMs. That orchestration gives them power but also fragility: a subtle corruption in decision-making can turn an assistant into a vector for exfiltration, sabotage, or lateral attack.

The “Lethal Trifecta” 
One of the most urgent lessons from 2025 is captured in The Economist’s notion of the “lethal trifecta”: because LLMs cannot reliably distinguish instructions from data at the token level, a malicious payload can be interpreted as control logic deep in the reasoning chain - even when perimeter filters would never see it. Replit, Amazon Q, and Gemini all had external guardrails in place when they failed, demonstrating that the weakness lies inside the decision loop.[1]

The Gemini Trifecta: A Case in Point
Tenable’s September 2025 disclosure of the “Gemini Trifecta” illustrates how context channels - logs, search history, and browsing - become hijack surfaces. These vectors bypass many classic defenses; Google has patched and reinforced sandboxing, hyperlink filtering, and output sanitization to close the gaps. These incidents emphasize that every input channel, not just user text, is now potentially dangerous.[2]

What Attackers Are Doing (Expanded)
Attack surfaces now include the internal decision topology, attention patterns, chain-of-thought nodes, and agent interdependencies. Notable attack types include:
  • Direct and indirect prompt injection
  • Agent hijacking and tool abuse
  • Worm-class propagation [3]
  • Multimodal or “stego” prompts [4]
  • Supply-chain or model poisoning
  • Guardrail bypass and over-defense tension
  • Reasoning-layer exploitation
  • Cognitive attacks (CIA+TA framework)
  • Complex multi-agent exploitation

The Updated Defensive Playbook: Three Layers, Not Two
To address this expanded threat model, defense must evolve beyond input/output filters to also protect the reasoning core.

Layer 1: Perimeter and Lifecycle Controls
  • Harden prompts
  • Input and output filtering
  • Tool constraints and allow-lists
  • Supply-chain scanning
  • Logging, observability, and escalation
  • Threat modeling, red teaming, agent identity and IAM
  • Containment and fail-safe kill switches

Layer 2: Reasoning-Layer Defenses (Internal Instrumented Protection)
Here resides Mountain Theory’s contribution and the frontier of innovation.  Mountain Theory’s AI Infrastructure Defense employs triple-agent architecture (Policy, Guardian, Adjudicator) to interpose within the reasoning process:  
  • Auditing chains of thought
  • Intercepting suspicious logic
  • Enforcing constraints on intent
  • Logging internal decision states.
By operating inside the reasoning loop before tools are invoked, Mountain Theory’s approach catches malicious deliberation early and provides audit trails of internal choices.[5]

Layer 3: Governance, Oversight, and Human-in-Loop Controls
  • Human approval gates for high-risk actions
  • Escalation and fallback paths
  • Kill switches for runaway or anomalous agent behavior
  • Explainable logs and forensic tracing of internal decisions

Tools and Products You Can Deploy
Perimeter and lifecycle tools include:
  • NVIDIA NeMo Guardrails
  • Microsoft Prompt Shields and Spotlighting
  • Google Layered Defenses for Gemini
  • Meta Llama Prompt Guard 2
  • Robust Intelligence AI Firewall
  • Protect AI (Guardian and ModelScan)
  • Lakera Gandalf
Reasoning-layer and internal-process tools include:
  • Mountain Theory AI Infrastructure Defense (Policy, Guardian, Adjudicator architecture)
  • LlamaFirewall (chain-of-thought auditing and code safety)
  • Emerging agent-embedded monitoring in CrowdStrike Threat AI and Charlotte AI
  • Experimental introspective anomaly detectors from academic work

Control Baseline (Reintegrated and Refined)
  • Threat-model your agent: define tools, data access, identities, and egress paths.
  • Isolate untrusted context: spotlight external inputs and separate secrets from external text.
  • Harden prompts, but do not rely solely on them: use concise, explicit instructions and reasoning-layer defenses.
  • Guard inputs and outputs: layered validators combining deterministic rules and LLM classifiers.
  • Constrain tool use: typed schemas, allow-lists, rate limits, human confirmations.
  • Use least privilege identities: separate identities per agent, rotate credentials, limit scope.
  • Scan the AI supply chain: model checks, SBOMs, artifact signing, and integrity verification.
  • Red-team continuously: include reasoning-level tests in bypass metrics and dwell time.
  • Plan for containment and oversight: kill switches, human overrides, explainability, and fallback logic.

Bottom Line: Defense Must Reach Inside
Classic edge defenses, such as validation and identity controls, remain necessary but insufficient. Reasoning-layer defenses, such as those pioneered by Mountain Theory, are crucial for detecting attacks that perimeter filters may miss. Governance, auditability, and human oversight must be woven into every AI agent architecture. Vendors like CrowdStrike, Palo Alto Networks, and Mountain Theory are converging toward AI-native security, where agents/frameworks/generative networks protect themselves.[6][7][8]

Endnotes
[1] The Economist. (September 27, 2025). 'Bad things come in threes: Why AI systems may never be secure, and what to do about it'. The Economist, p. 70. Retrieved from https://www.economist.com/science-and-technology/2025/09/22/why-ai-systems-may-never-be-secure-and-what-to-do-about-it
[2] Tenable. (September 30, 2025). 'The Trifecta: How Three New Gemini Vulnerabilities in Cloud Assist, Search Model, and Browsing Were Exploited'. Retrieved from https://www.tenable.com/blog/the-trifecta-how-three-new-gemini-vulnerabilities-in-cloud-assist-search-model-and-browsing
[3] In the context of agentic AI, a worm is a malicious prompt, payload, or policy-manipulation that propagates through the AI ecosystem (RAG stores, shared knowledge bases, email/attachments, plugin registries, agent-to-agent messages) and causes multiple agents or services to adopt and re-transmit the harmful payload or behavior.
[4] Steganographic prompts are malicious instructions hidden inside seemingly benign data—usually within non-textual or multi-modal content—so that they bypass conventional input filters but still get interpreted by a Large Language Model (LLM) or agent during processing.
[5] Mountain Theory. (2024). 'Emerging Threats to Artificial Intelligence Systems and Gaps in Current Security Measures'. Mountain Theory. Retrieved from https://www.mountaintheory.ai
[6] G7 Cyber Expert Group. (September 2025). 'Statement on Artificial Intelligence and Cybersecurity'. Retrieved from https://www.gov.uk/government/publications/g7-cyber-expert-group-statement-on-artificial-intelligence-and-cybersecurity-september-2025
[7] CrowdStrike. (September 16, 2025). 'Falcon Platform Fall 2025 Release and AI Detection and Response (AIDR)'. Retrieved from https://www.crowdstrike.com/en-us/press-releases/crowdstrike-unveils-falcon-platform-fall-release-to-lead-cybersecurity-into-agentic-era
[8] Palo Alto Networks. (July 22, 2025). 'Palo Alto Networks Completes Acquisition of Protect AI'. Retrieved from https://www.paloaltonetworks.com/company/press/2025/palo-alto-networks-completes-acquisition-of-protect-ai

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