CVE-2026-95394

Executive Summary

CVE-2026-95394 is a denial-of-service vulnerability in the Microsoft Network Monitor file parser affecting versions 4.6.0 through 4.6.8 and 4.4.0 through 4.4.18. The flaw is classified as CWE-606 (Unchecked Loop Condition) and is triggered when parsing a maliciously crafted capture file, causing an excessive loop that leads to resource exhaustion and application unavailability. The CVSS v3.1 score is 4.7 (Medium), with the attacker requiring local access and user interaction to exploit the vulnerability.

Technical Analysis

The vulnerability resides in the file parsing component of Microsoft Network Monitor. According to the NVD description, the issue is a "large loop" that occurs when processing certain input files. This aligns with CWE-606, which describes an unchecked loop condition where the number of iterations is not properly bounded by a trusted value. In the context of a file parser, this typically means the parser reads a count or length field from the input file and then uses it to control a loop without validating that the count is reasonable or that sufficient data remains in the file. An attacker can craft a file that specifies an extremely large iteration count, causing the parser to enter a loop that consumes excessive CPU cycles and memory, leading to a denial of service.

The attack surface is the file parsing interface of Microsoft Network Monitor. The parser is designed to read various network capture formats, and it processes attacker-supplied files. The vulnerability is not remotely exploitable without user interaction; it requires the victim to open a malicious file, which is consistent with the CVSS vector indicating UI:R (User Interaction Required) and AV:L (Local Attack Vector). The high attack complexity (AC:H) suggests that the attacker may need to overcome certain conditions for successful exploitation, such as crafting a file that passes initial validation but still triggers the loop.

Insufficient technical detail is available in the provided description to identify specific function names, file paths, or exact parsing routines. The vulnerability class—unchecked loop condition leading to resource exhaustion—is well understood and commonly found in parsers that handle binary formats with variable-length fields. No public proof-of-concept or exploit code is known at this time.

Exploitation Scenarios

1. Reconnaissance/target identification: An attacker identifies an environment where Microsoft Network Monitor versions 4.4.0–4.4.18 or 4.6.0–4.6.8 are in use. This may be done through network scanning for installed software, social engineering, or by targeting known users who process network capture files (e.g., network administrators, security analysts).

2. Crafting the malicious file: The attacker creates a specially crafted network capture file that triggers the unchecked loop condition. Since the exact file format is not specified in the description, the attacker would need to reverse-engineer the parser or rely on knowledge of the specific input format that leads to the large loop. The file is designed to cause the parser to iterate excessively, consuming CPU and memory.

3. Delivery and user interaction: The attacker delivers the malicious file to the victim, typically via email attachment, a download link, or a shared network location. The victim must open the file with Microsoft Network Monitor, satisfying the user interaction requirement.

4. Triggering the denial of service: Upon opening the file, the parser enters the large loop, causing the application to become unresponsive or crash. This can result in a denial of service on the affected system, potentially disrupting network monitoring and analysis activities.

5. Post-exploitation impact: The primary impact is availability loss—the application becomes unusable, and the system may experience resource exhaustion. There is no evidence of confidentiality or integrity impact, as the CVSS vector shows C:N and I:N. The attacker may use this as a diversion or as part of a larger attack chain, but the direct impact is limited to DoS.

No public PoC is available; the attack chain is inferred from the vulnerability class.

Impact Assessment

The CVSS v3.1 score is 4.7 (Medium), with the following subscores:

• Attack Vector (AV): Local (L) — the attacker must deliver a file to the victim's system.
• Attack Complexity (AC): High (H) — exploitation may require specific conditions or crafted input.
• Privileges Required (PR): None (N) — no authentication needed.
• User Interaction (UI): Required (R) — the victim must open the malicious file.
• Scope (S): Unchanged (U) — the impact is confined to the vulnerable component.
• Confidentiality (C): None (N) — no data exposure.
• Integrity (I): None (N) — no data modification.
• Availability (A): High (H) — the vulnerability causes a significant denial of service.

The business impact is primarily operational: network monitoring and troubleshooting capabilities are disrupted. Organizations relying on Microsoft Network Monitor for real-time analysis or forensic investigations may experience downtime and loss of visibility. The blast radius is limited to the system where the application is installed, but in shared environments, multiple users could be affected if the file is distributed. The EPSS score is not yet available, and there is no evidence of active exploitation in the wild or inclusion in CISA KEV.

Detection Guidance

Sigma Rule

title: Microsoft Network Monitor Denial of Service via Crafted File
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2026-95394 by monitoring for abnormal process termination or high resource usage of Microsoft Network Monitor.
author: Threat Intelligence Team
date: 2026-01-01
logsource:
  product: windows
  service: application
detection:
  selection:
    EventID: 1000
    Provider_Name: 'Application Error'
    Application: 'Netmon.exe'
  condition: selection
falsepositives:
  - Legitimate crashes due to other issues
level: medium

YARA Rule

rule CVE_2026_95394_NetworkMonitor_DoS
{
    meta:
        description = "Detects potential malicious network capture files targeting CVE-2026-95394"
        author = "Threat Intelligence Team"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-95394"
    strings:
        $magic = { 4D 53 4E 4D } // Hypothetical magic bytes for Network Monitor files; adjust as needed
    condition:
        $magic at 0 and filesize < 10MB
}

Note: The YARA rule above is a template. Specific file format indicators are not provided in the vulnerability description, so the rule may need refinement based on actual file format analysis.

Suricata IDS Rule

alert tcp any any -> any any (msg:"CVE-2026-95394 Microsoft Network Monitor Denial of Service Attempt"; flow:to_client; file_data; content:"|4D 53 4E 4D|"; depth:4; filestore; sid:1000001; rev:1;)

This rule detects the transfer of files with a potential Network Monitor magic header. It is a heuristic and may require tuning.

Elastic Detection

process where process.name == "Netmon.exe" and event.action == "crash" and process.exit_code != 0

Detects crashes of the Network Monitor process, which could indicate exploitation.

Splunk SPL Query

index=windows source="WinEventLog:Application" EventCode=1000 Provider_Name="Application Error" Application="Netmon.exe"
| stats count by host, _time
| where count > 5

Alerts on multiple crashes of Netmon.exe within a short period.

Wazuh OSSEC Rule

<group name="windows,">
  <rule id="100001" level="10">
    <if_sid>60000</if_sid>
    <field name="win.system.providerName">Application Error</field>
    <field name="win.system.application">Netmon.exe</field>
    <description>CVE-2026-95394: Microsoft Network Monitor possible DoS attempt detected</description>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations:

   • Avoid opening untrusted or unknown network capture files with Microsoft Network Monitor.
   • Implement email and web filtering to block potentially malicious capture files.
   • Restrict user privileges to limit the impact of a crash.
   • Monitor for abnormal resource usage or crashes of Netmon.exe.

2. Patch/upgrade steps:

   • No official patch is available at this time. Monitor Microsoft's security advisories and update to a fixed version as soon as it is released.
   • Consider using alternative network analysis tools that are not affected.

3. Long-term hardening:

   • Conduct regular vulnerability assessments and patch management.
   • Apply the principle of least privilege for users who handle network capture files.
   • Implement application whitelisting to prevent execution of unauthorized tools.

References

• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-95394
• CWE-606: https://cwe.mitre.org/data/definitions/606.html
• Microsoft Security Response Center: https://msrc.microsoft.com/ (monitor for updates)
• No known threat actor campaigns or exploit-in-the-wild evidence at this time.