CVE-2026-33921 in Npcap
Summary
by MITRE • 08/11/2026
The Windows installer deployed Npcap leaving its access restriction option at the insecure default value, so the driver was accessible to every local user of the host instead of being restricted to administrators only. A local user without administrative privileges could use the Npcap driver to capture the traffic reaching the host, which discloses information belonging both to the host and to other systems on the same network segment, and to send arbitrary raw packets on that segment.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 08/11/2026
The vulnerability described represents a critical access control flaw in the Npcap network driver installation process on Windows systems. This issue stems from the default configuration settings that fail to properly restrict driver access permissions, creating an insecure baseline that undermines fundamental security principles of least privilege and principle of minimal access. The problem manifests when the Windows installer deploys Npcap with its access restriction option set to an insecure default value, effectively allowing any local user account to interact with the network driver regardless of administrative privileges. This configuration directly violates security best practices established in industry standards such as those outlined in CWE-284, which addresses improper access control mechanisms in software applications.
The technical implications of this vulnerability extend beyond simple privilege escalation to encompass comprehensive network monitoring and manipulation capabilities. A local user without administrative rights can leverage the improperly configured Npcap driver to perform packet capture operations on the host system, potentially exposing sensitive network traffic that may include credentials, personal information, financial data, or proprietary communications. The vulnerability also enables the execution of arbitrary raw packet transmission on the local network segment, allowing attackers to craft and inject malicious packets into the network infrastructure. This dual capability for both passive monitoring and active network manipulation creates a significant threat vector that can facilitate various attack scenarios including man-in-the-middle attacks, network reconnaissance, and lateral movement within compromised environments.
The operational impact of this vulnerability is substantial across multiple security domains and affects organizations of varying sizes. Network administrators face increased risk of data exposure through unauthorized packet capture activities that could compromise sensitive communications between the host system and other devices on the same network segment. The ability to send arbitrary raw packets also opens possibilities for network disruption, injection attacks, and potential exploitation of vulnerabilities in network protocols or applications. This issue particularly affects environments where multiple users share the same physical or virtual machines, as well as systems where user accounts may be compromised through social engineering, credential theft, or other attack vectors. The vulnerability can be exploited by both malicious insiders and external attackers who have gained local access to a system, making it a significant concern for organizations implementing zero-trust security models that rely on strict access controls.
Mitigation strategies should focus on immediate remediation of the installer configuration followed by comprehensive security hardening practices. Organizations must ensure that Npcap installations properly enforce access restrictions through automated deployment scripts or configuration management tools that explicitly set driver permissions to restrict access to administrative users only. Security policies should include regular auditing of installed network drivers and their associated access controls to identify any deviations from secure baselines. System administrators should implement monitoring solutions that can detect unauthorized packet capture activities or raw packet transmission attempts, which aligns with ATT&CK technique T1046 for network service scanning and T1071 for application layer protocol usage. The vulnerability also highlights the importance of proper software supply chain security practices and the need for regular security assessments of third-party network tools to ensure they do not introduce unintended access control weaknesses into enterprise environments.