Performing penetration testing and audits in an HPC environment requires a fundamentally different approach than corporate IT. The Golden Rule of HPC Security Testing is "Do No Harm." A standard vulnerability scan (like Nessus or Qualys) running default policies can easily saturate a login node's network interface or crash a fragile legacy scheduler, resulting in lost research cycles and furious users.

Here is a tailored strategy for executing robust penetration tests and audits without disrupting scientific throughput.

1. The Strategy: "Inside-Out" vs. "Outside-In"

HPC security relies on a "hard outer shell, soft creamy center" model. Your testing must validate both the hardness of the shell and the segmentation of the internal network.

Testing Zone	Scope	Aggression Level	Primary Risk
Perimeter	Login Nodes, DTNs, VPN Gateways	High	Brute-force, SSH exploitation
Control Plane	Schedulers (Slurm/PBS), Management Nodes	Low / Manual	DoS, crashing the scheduler
Data Plane	Parallel Filesystems (Lustre/GPFS)	Medium	IOPS saturation, data corruption
Compute Fabric	Compute Nodes, InfiniBand/Omni-Path	Low	Latency spikes affecting running jobs

Here is a tailored strategy for executing robust penetration tests and audits without disrupting scientific throughput.

1. The Strategy: "Inside-Out" vs. "Outside-In"

HPC security relies on a "hard outer shell, soft creamy center" model. Your testing must validate both the hardness of the shell and the segmentation of the internal network.

Testing Zone	Scope	Aggression Level	Primary Risk
Perimeter	Login Nodes, DTNs, VPN Gateways	High	Brute-force, SSH exploitation
Control Plane	Schedulers (Slurm/PBS), Management Nodes	Low / Manual	DoS, crashing the scheduler
Data Plane	Parallel Filesystems (Lustre/GPFS)	Medium	IOPS saturation, data corruption
Compute Fabric	Compute Nodes, InfiniBand/Omni-Path	Low	Latency spikes affecting running jobs

2. Comprehensive Audit Framework (White Box)

Before launching active attacks, perform a configuration audit. This reveals the "low hanging fruit" without risking downtime.

A. Scheduler Audit (Slurm/PBS/LSF)

The scheduler is the most critical attack surface for privilege escalation.

Prolog/Epilog Scripts: Audit these scripts for unsafe file handling. If a user can manipulate a file that the Prolog script (running as root) executes, they own the node.
Resource Limits: Verify MaxSubmitJobs and MaxRSS to prevent a single user from accidentally (or maliciously) performing a Denial of Service (DoS) on the scheduler database.
Cleartext Credentials: Check job submission scripts for hardcoded passwords or API tokens left by researchers automating their workflows.

B. Storage & Data Governance Audit

World-Readable Data: Scan the parallel filesystem for sensitive data with world-readable permissions (chmod 777). Researchers often open permissions to share data and forget to close them.
Orphaned Data: Identify "scratch" data owned by users who have left the institution.
NFS Exports: Ensure management exports (like /home or /software) are root_squashed and restricted to specific IP ranges.

C. Network Segmentation Verification

The "Science DMZ" Check: Verify that Data Transfer Nodes (DTNs) bypass the firewall only for specific high-speed ports, but are locked down on management ports (SSH/Web).
Compute Isolation: Confirm that compute nodes cannot reach the public internet directly. Attempt to curl an external site from a compute job; if it succeeds, your isolation has failed.

3. Active Penetration Testing (Red Team)

Once the audit is complete, move to active testing. Notify the PIs (Principal Investigators) of the schedule, as these tests might trigger false-positive alarms or minor latency.

Phase 1: Perimeter Breach (The Login Node)

SSH Fuzzing: Test the SSH daemon for resistance to brute force. Verify fail2ban or similar IP-banning tools kick in immediately.
MFA Bypass: Attempt to access the cluster via alternative entry points (e.g., VNC sessions, web portals like Open OnDemand, or legacy FTP servers) that might lack the MFA enforcement present on SSH.

Phase 2: Lateral Movement (The Compute Node)

Container Breakout: Launch a malicious job using Singularity/Apptainer. Attempt to escalate privileges or mount host directories that should be restricted.
Shared Memory Snooping: On a shared compute node, run a job that attempts to read the memory or scratch space of another user's job running on the same core.
InfiniBand Sniffing: If you have root on one node (simulating a compromised node), attempt to sniff RDMA traffic. (Note: This is advanced but critical for high-security clusters).

Phase 3: Privilege Escalation

"Dirty Cow" & Kernel Exploits: Compute nodes often run older kernels to maintain driver compatibility. Test if a standard user can run a local kernel exploit to gain root on a compute node.
Services Exploitation: Attack internal services that typically have no authentication because "they are inside the firewall" (e.g., a license server or a monitoring agent).

4. specialized Tooling for HPC

Standard tools (Metasploit, Nessus) are useful but blunt. Supplement them with:

ClusterShell / pdsh: For running audit commands across 1,000 nodes simultaneously to check for configuration drift.
Red Hat / NIST OpenSCAP: For automated compliance checking against a security baseline (e.g., STIGs) specifically for RHEL/CentOS.
Custom Slurm Scripts: Write scripts to specifically fuzz sbatch parameters.

5. Reporting & Remediation

When reporting findings to HPC management, frame vulnerabilities in terms of Scientific Impact:

Bad: "Compute node 50 has an unpatched kernel."
Good: "An unpatched vulnerability on Compute Node 50 allows a user to crash the node, potentially ruining a 2-week simulation and wasting $5,000 in compute credits."