Executive Summary
In May 2026, security researcher Kim Dvash from Israel Aerospace Industries unveiled 'GhostLock,' a proof-of-concept tool that exploits the Windows 'CreateFileW' API to deny access to files on local and SMB network shares. By setting the 'dwShareMode' parameter to zero, GhostLock opens files in exclusive mode, preventing other processes from accessing them and resulting in 'STATUS_SHARING_VIOLATION' errors. This technique can be executed by standard domain users without elevated privileges, potentially leading to significant operational disruptions.
The release of GhostLock highlights a critical vulnerability in Windows file handling mechanisms, emphasizing the need for organizations to reassess their security protocols. As attackers increasingly leverage legitimate system APIs for malicious purposes, it is imperative for IT departments to implement robust monitoring and mitigation strategies to prevent such denial-of-service attacks.
Why This Matters Now
The emergence of GhostLock underscores the urgency for organizations to address vulnerabilities in Windows file handling, as attackers can exploit these to disrupt operations without elevated privileges.
Attack Path Analysis
An attacker utilizes the GhostLock tool to exploit the Windows CreateFileW API, opening numerous files with exclusive access to deny other processes access. This action disrupts file availability, causing operational downtime. The attack does not require elevated privileges and can be executed by standard domain users. Once the attack ceases or the system is rebooted, file access is restored.
Kill Chain Progression
Initial Compromise
Description
The attacker gains access to a system as a standard domain user, potentially through phishing or exploiting weak credentials.
MITRE ATT&CK® Techniques
Endpoint Denial of Service
Valid Accounts
Impair Defenses: Disable or Modify Tools
Application Layer Protocol: Web Protocols
Remote Services: SMB/Windows Admin Shares
Potential Compliance Exposure
Mapping incident impact across multiple compliance frameworks.
PCI DSS 4.0 – Change Control Processes
Control ID: 6.4.1
NYDFS 23 NYCRR 500 – Cybersecurity Policy
Control ID: 500.03
DORA – ICT Risk Management Framework
Control ID: Article 5
CISA ZTMM 2.0 – Identity and Access Management
Control ID: 3.1
NIS2 Directive – Security Measures
Control ID: Article 21
Sector Implications
Industry-specific impact of the vulnerabilities, including operational, regulatory, and cloud security risks.
Financial Services
GhostLock denial-of-service attacks targeting SMB shares could disrupt critical financial data access, trading operations, and compliance reporting systems requiring continuous availability.
Health Care / Life Sciences
File access blocking via Windows API abuse threatens patient record availability, medical imaging systems, and HIPAA compliance for healthcare data accessibility requirements.
Government Administration
SMB network share disruptions could paralyze government file systems, citizen services, and inter-agency data sharing while masking lateral movement activities.
Information Technology/IT
IT organizations face direct exposure to GhostLock attacks on file servers, development environments, and client networks lacking proper SMB security controls.
Sources
- New GhostLock tool abuses Windows API to block file accesshttps://www.bleepingcomputer.com/news/security/new-ghostlock-tool-abuses-windows-api-to-block-file-access/Verified
- GitHub - kimd155/GhostLock: SMB deny-share handle research toolhttps://github.com/kimd155/ghostlockVerified
- CreateFileW function (fileapi.h) - Win32 apps | Microsoft Learnhttps://learn.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilewVerified
Frequently Asked Questions
Cloud Native Security Fabric Mitigations and ControlsCNSF
Aviatrix Zero Trust CNSF is relevant to this incident as it could likely limit the attacker's ability to move laterally and control compromised systems, thereby reducing the overall impact and blast radius of the attack.
Control: Cloud Native Security Fabric (CNSF)
Mitigation: The attacker's initial access may be constrained, reducing the likelihood of unauthorized entry.
Control: Zero Trust Segmentation
Mitigation: The attacker's ability to escalate privileges may be limited, reducing the scope of potential damage.
Control: East-West Traffic Security
Mitigation: The attacker's lateral movement could be restricted, limiting the spread of the attack across systems.
Control: Multicloud Visibility & Control
Mitigation: The attacker's command and control communications may be detected and disrupted, limiting their ability to manage the attack.
Control: Egress Security & Policy Enforcement
Mitigation: The attacker's ability to exfiltrate data may be constrained, reducing the risk of data loss.
The overall impact of the attack may be reduced, limiting operational disruption.
Impact at a Glance
Affected Business Functions
- File Access Management
- Network File Sharing
- Data Availability
Estimated downtime: 1 days
Estimated loss: N/A
No data exposure; the attack results in temporary denial of access to files without data loss.
Recommended Actions
Key Takeaways & Next Steps
- • Implement Zero Trust Segmentation to restrict lateral movement and limit the attacker's ability to propagate the attack across systems.
- • Deploy Threat Detection & Anomaly Response mechanisms to identify and respond to unusual file access patterns indicative of such attacks.
- • Enforce strict access controls and monitor for unauthorized file access attempts to prevent exploitation of file-sharing modes.
- • Educate users on recognizing phishing attempts and enforce strong password policies to reduce the risk of initial compromise.
- • Regularly review and update security policies to address emerging threats and ensure comprehensive protection against denial-of-service attacks.
