Full Report
The death of blocklisting and resurrection of positive controls
Analysis Summary
# Best Practices: Execution Runtime Security (Positive Control Model)
## Overview
These practices address the shift from reactive, signature-based security (blocklisting) to a deterministic, **"Default-Deny"** architecture. This transition is essential to counter Agentic AI, which can generate zero-day exploits, chain legitimate APIs, and execute multi-stage attacks at machine speeds that bypass traditional detection-based (negative) security models.
## Key Recommendations
### Immediate Actions
1. **Identify Critical Assets:** Catalog high-value servers, cloud workloads, and environments where AI agents or automated service accounts operate.
2. **Audit Native Tool Usage:** Review the use of "Living off the Land" binaries (e.g., PowerShell, `vssadmin`, `wmic`) to determine which are strictly necessary for business operations.
3. **Enable Discovery Mode:** Deploy runtime monitoring tools in "audit-only" mode to baseline known-good behaviors without blocking legitimate traffic.
### Short-term Improvements (1-3 months)
1. **Transition to Cryptographic Allowlisting:** Move away from static hash-based lists to trust-based approvals using **Trusted Publisher** certificates (e.g., only allowing binaries signed by Microsoft, VMware, or internal CAs).
2. **Enforce Process-Level Restrictions:** Implement rules that prevent legitimate applications from spawning unauthorized child processes (e.g., blocking Office apps from launching PowerShell).
3. **Implement Memory Protection:** Enable runtime controls that prevent unauthorized code injection into the memory space of trusted processes.
### Long-term Strategy (3+ months)
1. **Full Deterministic Enforcement:** Shift from "Alerting" to "Blocking" for all non-verified execution paths across the production environment.
2. **Automated Policy Lifecycle:** Integrate allowlisting into the CI/CD pipeline so that new, authorized code is automatically cryptographically verified and added to the allowlist upon deployment.
3. **Agentic AI Guardrails:** Establish specific runtime boundaries for autonomous agents, limiting their ability to interact with the OS kernel or sensitive file systems regardless of their identity permissions.
## Implementation Guidance
### For Small Organizations
- Focus on locking down the most critical servers first.
- Leverage cloud-driven reputation services to reduce the manual burden of managing allowlists.
- Prioritize "Trusted Publisher" rules over individual file hashes to minimize maintenance.
### For Medium Organizations
- Implement **File Integrity Monitoring (FIM)** alongside runtime controls to track unauthorized changes.
- Use group-based policies to differentiate between developer needs (more flexible) and administrative/production needs (more rigid).
- Utilize "Maintenance Mode" features during scheduled updates to prevent false positives.
### For Large Enterprises
- Deploy centralized management (e.g., Carbon Black App Control) to handle heterogeneous environments (Windows, Linux, Cloud).
- Integrate runtime security events with the SOC's SIEM/XDR to provide context on blocked execution attempts.
- Adopt a "Global Drift" strategy: alert on any variation from a "Gold Image" across distributed data centers.
## Configuration Examples
While specific code varies by vendor, the logic follows this deterministic flow:
* **Rule Type:** Trusted Publisher
* *Action:* Allow
* *Condition:* Certificate Subject matches `O=Microsoft Corporation` AND `Status=Valid`.
* **Rule Type:** Path Restriction
* *Action:* Block & Log
* *Condition:* Path matches `\temp\*` AND Execution attempted.
* **Rule Type:** Process Guard
* *Action:* Terminate
* *Condition:* `SourceProcess=sqlservr.exe` attempts to launch `cmd.exe`.
## Compliance Alignment
- **NIST SP 800-53:** CM-7 (Least Functionality) and SI-7 (Software, Firmware, and Information Integrity).
- **CIS Controls:** Control 2 (Inventory and Control of Software Assets).
- **ISO/IEC 27001:** A.12.5.1 (Installation of software on operational systems).
## Common Pitfalls to Avoid
- **Static Hash Overload:** Do not rely solely on MD5/SHA-256 hashes; they change with every software update, leading to "update fatigue."
- **Over-Privileged AI:** Avoid assuming an AI agent is safe just because it uses a valid Service Account; identity is not a substitute for execution control.
- **Incomplete Baselines:** Switching to "Block" mode before fully understanding the environment's normal operational execution paths.
## Resources
- **Frameworks:** [NIST Guide to Application Whitelisting](https://nvlpubs.nist.gov/nistpubs/specialpublications/nist.sp.800-167.pdf) (Defanged)
- **Tools:** Carbon Black App Control, Microsoft AppLocker, Windows Defender Application Control (WDAC).
- **Concepts:** [Zero Trust Architecture (NIST 800-207)](https://csrc.nist.gov/publications/detail/sp/800-207/final) (Defanged)