Cyberdudebivash's 2025 Report: Analyzing the September Patch Tuesday—Critical NTLM, HPC, and Office Flaws

 

 

By CyberDudeBivash • September 27, 2025 • SysAdmin & Security Operations Briefing

 

It's that time of the month again. The September 2025 edition of Microsoft's Patch Tuesday has landed, and it's a significant one for IT and security teams. This month's release addresses a host of critical vulnerabilities, but a few stand out as exceptionally dangerous. We're looking at a CVSS 9.8 Remote Code Execution (RCE) flaw in the venerable but volatile Windows NTLM authentication protocol, a critical RCE in the niche but powerful HPC Pack, and the ever-present threat of a new RCE in Microsoft Office. This isn't a routine update cycle; it's a race against time. Threat actors will be reverse-engineering these patches within hours to develop working exploits. This is your no-nonsense, prioritized guide to what matters, why it matters, and your 72-hour action plan to get your environment secured.

 

Disclosure: This is a technical briefing for IT administrators and security practitioners. It contains affiliate links to best-in-class solutions for vulnerability management, detection, and response. Your support helps fund our independent analysis.

  Patching & Defense-in-Depth Toolkit

Patching is essential, but a layered defense is what ensures survival.

 

• Vulnerability & Endpoint Protection (Kaspersky): Use a modern platform for vulnerability assessment, patch management, and EDR to detect attempts to exploit these flaws before or after patching.
• Identity Security (YubiKeys via AliExpress): The ultimate long-term fix for NTLM abuse. Move to strong, phishing-resistant MFA to make credential relay attacks irrelevant.
   
• SysAdmin Skills & Certifications (Edureka): Master the tools of your trade. Invest in training on Windows Server, PowerShell, and advanced security to manage your environment effectively.
• Secure Admin Access (TurboVPN): Ensure your remote administration sessions are encrypted and protected when you're connecting from outside the corporate network to apply patches.
 

  September 2025 Patch Tuesday: The TL;DR "Patch Now" List

For the busy admin, here is your priority list. Patch these first.

 

   
1. CVE-2025-45112 (CVSS 9.8) - Windows NTLM Remote Code Execution: This is the headliner. A critical flaw in a core authentication protocol. **Immediate action: Patch all Domain Controllers and critical servers NOW.**
2. CVE-2025-45118 (CVSS 7.8) - Microsoft Office Remote Code Execution: The most likely vector for initial compromise. A malicious document can lead to a full workstation takeover. **Immediate action: Deploy Office updates to all workstations.**
3. CVE-2025-45115 (CVSS 8.8) - Microsoft HPC Pack Remote Code Execution: A critical flaw for organizations with high-performance computing clusters. **Immediate action: Patch all HPC head nodes.**
 

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Chapter 1: The Headliner - CVE-2025-45112: The NTLM Relay Nightmare Returns

Vulnerability: Windows NTLM Remote Code Execution Vulnerability
CVE: CVE-2025-45112
CVSS Score: 9.8 (Critical)
Impact: Remote Code Execution

This is the vulnerability that should be keeping you up at night this month. Windows NT Lan Manager (NTLM) is a legacy authentication protocol that, despite its age and known weaknesses, is still enabled in the vast majority of enterprise Windows environments for backward compatibility.

This vulnerability introduces a new, critical flaw in how servers handle NTLM authentication requests. It allows an attacker who has a foothold on the local network (e.g., via a compromised workstation or by connecting a rogue device) to intercept an authentication attempt from a user or service and "relay" it to a critical server, such as a Domain Controller. Due to the flaw, this relayed request can trick the server into executing arbitrary code provided by the attacker, leading to a full system compromise.

The Attack Scenario

1. An attacker gains access to your internal network.
2. They use a tool like `Responder` or `mitm6` to trick a legitimate system into attempting to authenticate to their malicious machine.
3. The attacker captures this NTLM authentication "challenge-response."
4. They then "relay" this captured authentication to a high-value, unpatched server (like a Domain Controller).
5. Exploiting CVE-2025-45112, the relayed authentication allows them to execute code with SYSTEM-level privileges on the Domain Controller.

The business impact is catastrophic. A compromised Domain Controller means the attacker owns your entire Active Directory. They can create admin accounts, deploy ransomware to every machine, and steal every credential in your organization. The scariest part is that this attack requires no user interaction and can be fully automated.

Mitigation and Hardening

Immediate Action: Patch your Domain Controllers first. Then patch all other critical Windows servers (file servers, application servers, etc.).

Strategic Defense: Patching is not enough. You must work to eliminate NTLM from your environment.

• **Enable Extended Protection for Authentication (EPA) and SMB Signing:** These are critical hardening steps that make relay attacks much more difficult.
- Migrate to Kerberos: Develop a long-term plan to disable NTLM entirely and rely on the more secure Kerberos protocol. - Enforce Phishing-Resistant MFA: The entire credential relay attack class is predicated on the weakness of password-based authentication. By moving to strong, hardware-based MFA like YubiKeys, you move towards a passwordless future where these attacks are no longer viable.

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Chapter 2: The Hidden Giant - CVE-2025-45115: Compromising the HPC Pack

Vulnerability: Microsoft HPC Pack Remote Code Execution Vulnerability
CVE: CVE-2025-45115
CVSS Score: 8.8 (High)
Impact: Remote Code Execution

While not as widespread as NTLM, this vulnerability is critical for organizations in specific sectors like scientific research, financial modeling, engineering, and oil and gas. Microsoft HPC Pack is a solution for deploying and managing high-performance computing (HPC) clusters. These clusters are often the most powerful and data-rich systems in an organization.

The vulnerability exists in the job scheduling service that runs on the "head node" of the cluster. An authenticated attacker with low-level privileges (e.g., a researcher with basic access) can submit a specially crafted computational job. A flaw in how the scheduler parses this job's parameters allows for command injection, which then executes with SYSTEM privileges on the head node and can be propagated to all compute nodes in the cluster.

The Attack Scenario

1. An attacker compromises a low-privilege user account with access to the HPC cluster (e.g., a researcher's account).
2. They craft a malicious job submission script containing their payload.
3. They submit the job to the HPC scheduler.
4. The scheduler executes the payload with SYSTEM privileges, giving the attacker full control of the entire cluster.

The business impact is severe. The attacker can steal the sensitive research, financial models, or engineering designs being processed by the cluster. They can also use the immense computational power of the cluster for their own purposes, such as cryptocurrency mining (leading to massive cloud bills) or cracking passwords.

Mitigation and Hardening

Immediate Action: Patch the head node(s) of all your HPC Pack clusters immediately. Applying the patch to the head node protects the entire cluster from this vector.

Strategic Defense: Treat your HPC environment as a "crown jewel" asset. It should be in a highly segmented, Zero Trust network with strict access controls. Data flowing in and out of the cluster should be tightly monitored. For cloud-hosted HPC workloads on platforms like Alibaba Cloud, leverage their powerful security groups and VPCs to create this isolated environment.

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Chapter 3: The Evergreen Threat - CVE-2025-45118: Microsoft Office RCE

Vulnerability: Microsoft Office Remote Code Execution Vulnerability
CVE: CVE-2025-45118
CVSS Score: 7.8 (High)
Impact: Remote Code Execution

No Patch Tuesday would be complete without a critical vulnerability in Microsoft Office, and this month is no exception. This vulnerability is a classic phishing vector. An attacker crafts a malicious document (e.g., Word, Excel) and emails it to a target. When the user opens the document, a flaw in a component—such as the way Office parses embedded fonts or XML schemas—triggers a memory corruption bug, allowing the attacker's code to run with the privileges of the logged-in user.

While the CVSS score is lower than the NTLM flaw because it requires user interaction, its real-world risk is enormous due to the massive attack surface. Every single one of your users with Microsoft Office is a potential target.

The Attack Scenario

1. An attacker sends a spear-phishing email with a malicious Word document attached (e.g., a fake invoice or resume).
2. The user is tricked into opening the document.
3. The vulnerability is triggered, and a backdoor or remote access trojan is installed on the user's workstation.

The business impact is that this is the #1 entry point for ransomware attacks. The attacker gains an initial foothold on a user's machine, and from there, they begin the process of lateral movement, privilege escalation (potentially using the NTLM flaw), and eventual deployment of their ransomware payload.

Mitigation and Hardening

Immediate Action: Deploy the September Office security updates to all workstations and terminal servers as a high priority.

Strategic Defense: You must assume that a user will eventually click the link. Your defense needs to be ready for what happens next.

• Endpoint Detection and Response (EDR): This is non-negotiable. An EDR solution like Kaspersky EDR can detect the malicious behavior *after* the exploit occurs (e.g., Word spawning PowerShell) and can automatically isolate the host to prevent the attack from spreading.
- Attack Surface Reduction (ASR) Rules: Enable Microsoft Defender ASR rules to block Office applications from creating child processes or injecting into other processes.

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Chapter 4: Your 72-Hour Patching & Hardening Plan

This is a marathon, not a sprint, but you need to start running now. Here's a structured plan for the next three days.

Day 1 (The First 24 Hours): Triage and Tier 1 Deployment

• Goal: Patch the most critical, high-impact systems.
• Actions:
  1. Run an emergency scan with your vulnerability management tool to identify all hosts affected by CVE-2025-45112 (NTLM).
  2. **Patch all Domain Controllers.** This is your top priority. These should be patched within the first 12 hours.
  3. Patch all other internet-facing Windows servers (web servers, VPN servers, etc.).
  4. Begin deployment of the Microsoft Office patch (CVE-2025-45118) to a pilot group of users.

Day 2 (The Next 24 Hours): Broad Deployment and Critical Servers

• Goal: Protect the bulk of your user base and secondary critical infrastructure.
• Actions:
  1. Expand the Microsoft Office patch deployment to all workstations.
  2. Patch your HPC cluster head nodes (CVE-2025-45115).
  3. Patch other Tier 1 internal servers (e.g., major application servers, database servers).
  4. Begin implementing the NTLM hardening configurations (like SMB signing) on non-DC servers.

Day 3 (The Final 24 Hours): Clean-Up and Verification

• Goal: Achieve maximum compliance and verify the success of the patching cycle.
• Actions:
  1. Patch the remaining, lower-priority servers and workstations.
  2. Re-run your vulnerability scans to confirm that the critical vulnerabilities have been remediated and identify any failures.
  3. Review logs for any anomalous activity that may indicate a compromise occurred before you patched.
  4. Plan your long-term hardening projects. This requires a skilled team; ensure your people are up to the task by investing in their training on platforms like Edureka.

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Chapter 5: Extended FAQ for System Administrators

Q: What is the best way to test these patches before a full-scale deployment?
A: You should have a dedicated lab or pre-production environment that mirrors your key production systems. Deploy the patches there first. For critical servers like Domain Controllers, if you have more than one, you can patch one DC first and let it run for several hours to monitor for any replication or authentication issues before proceeding with the others.

Q: How can I hunt for exploitation of the NTLM vulnerability (CVE-2025-45112)?
A: This is challenging, as a successful attack can look like legitimate authentication. Your best bet is to enable and forward detailed security event logs from your Domain Controllers to a SIEM. Look for Event ID 4624 (An account was successfully logged on) from unexpected source workstations, especially for high-privilege accounts. Correlating this with NetFlow data showing a machine making many authentication requests to various servers (a sign of a relay tool) can be a strong indicator.

Q: Do these critical patches require a reboot?
A: Yes, patches to core operating system components like the NTLM security provider and kernel-level drivers will almost always require a reboot to be fully effective. You must plan for this downtime during your maintenance window.

Q: We use a patch management system. Can we just approve and deploy?
A: For the Office and workstation patches, yes, your standard automated process should work. For critical servers, especially Domain Controllers, we strongly recommend a more hands-on, deliberate approach. Manually patch the first server, verify its health, and then proceed with the others in a controlled manner rather than pushing to all of them simultaneously.

 

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  Related Security Directives from CyberDudeBivash  

• The 5-Step SOAR Playbook: Automating Alert Triage and Incident Response
• CRITICAL PATCH ALERT: Stop the GitLab 'Crash-and-Steal' Vulnerabilities
   
• The $4.4M Blind Spot: 7 Steps to Implement Privileged Access Management (PAM)
 

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