THREAT OVERVIEW

Microsoft has released its September 2025 Patch Tuesday updates, addressing 81 security vulnerabilities, Severity: 10 Critical, 71 Important across multiple product lines such as Windows, Microsoft Office, Azure, SQL Server, Windows Defender, and related components . This release includes two zero-day vulnerabilities that are confirmed to be actively exploited in the wild. The scope of these patches covers widely used products and services, making immediate patching a priority for all enterprise and consumer environments.

KEY VULNERABILITIES

Zero-Day Vulnerabilities

1. CVE-2025-55234 – SMB Elevation of Privilege

o Affects: Windows Server Message Block (SMB)

o Risk: Enables relay attacks, allowing attackers to escalate privileges on affected systems.

o Impact: High risk due to SMB’s widespread use for file sharing and authentication.

o Action: Patch immediately on all Windows systems.

2. CVE-2024-21907 – Newtonsoft.Json Denial of Service

o Affects: Newtonsoft.Json framework used in SQL Server and .NET applications

o Risk: Crafted input to JsonConvert.DeserializeObject can trigger a StackOverflow exception, crashing the application.

o Impact: Remote unauthenticated attackers can exploit this flaw against SQL Server instances.

o Action: Apply updates and review applications using Newtonsoft.Json.

Other Critical Vulnerabilities

• CVE-2025-54918 – Windows NTLM EoP: Improper authentication allows privilege escalation over the network.

• CVE-2025-55226, CVE-2025-55228, CVE-2025-55236 – Windows Graphics Kernel/Component RCE: Race condition flaws allowing arbitrary code execution.

• CVE-2025-54910 – Microsoft Office RCE: Heap-based buffer overflow permitting remote code execution.

• CVE-2025-55224 – Windows Hyper-V RCE: Race condition vulnerability enabling code execution in virtualized environments.

Vulnerability Breakdown by Type

• Elevation of Privilege (EoP): 38

• Remote Code Execution (RCE): 22

• Information Disclosure: 14

• Denial of Service (DoS): 4

• Security Feature Bypass: 2

• Spoofing: 1

IMPACT

Successful exploitation of these vulnerabilities could allow:

• Unauthorized privilege escalation

• Remote execution of arbitrary code

• Application or service crashes (DoS)

• Exposure of sensitive data

Given the active exploitation of CVE-2025-55234 and the widespread deployment of impacted products (Windows SMB, SQL Server, Office, Hyper-V), the potential for widespread compromise is critical.

RECOMMENDATION

1. Apply Patches Immediately

o Prioritize SMB, NTLM, Graphics Kernel, and Hyper-V updates.

o Patch SQL Server environments using Newtonsoft.Json.

o Ensure Office productivity applications are updated to mitigate RCE risks.

2. Mitigation & Hardening

o Restrict SMB exposure to untrusted networks.

o Monitor for abnormal authentication requests indicative of relay attacks.

o Apply least-privilege principles for service accounts.

3. Detection & Monitoring

o Deploy updated signatures from Microsoft Defender and other security tools.

o Monitor SIEM logs for exploitation attempts targeting SMB, NTLM, and SQL Server.

o Check for abnormal process execution from Office applications.

4. Business Continuity

o Plan patch deployment in stages to reduce downtime.

o Test patches in staging before broad rollout where possible.

REFERENCES

• Microsoft Security Response Center (MSRC)

• GBhackers

• Tenable

• SL-CSIRT

Action Required:

All system administrators and IT security teams should review and apply September 2025 Microsoft updates immediately. Prioritize internet-facing systems and high-value assets to reduce risk from active exploitation.