CVE-2026-107039 in NetGuard
Summary
by MITRE • 10/29/2026
Insecure permissions in the ActivityMain component of M66B/Marcel Bokhorst NetGuard no-root firewall versionCode 2026080101/versionName 2.337 allows unauthorized attackers to arbitrarily force a device reset or Denial of Service (DoS).
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Analysis
by VulDB Data Team • 10/29/2026
The vulnerability identified in the ActivityMain component of Marcel Bokhorst NetGuard, specifically within version code 2026080101 and version name 2.337, represents a critical failure in access control mechanisms that governs sensitive device management functions. As an open-source no-root firewall application for Android devices, NetGuard relies heavily on user interaction to manage network rules and system configurations. The ActivityMain component serves as the primary interface for these operations, handling high-privilege actions such as resetting application settings or restoring default states. In this specific instance, insecure permissions associated with this activity allow an unauthorized attacker to trigger a device reset without proper authentication or authorization checks. This flaw fundamentally undermines the integrity of the security tool itself, transforming it from a protective measure into a potential vector for disruption.
From a technical perspective, this issue stems from improper configuration of Android Intent filters and permission declarations within the application manifest. Typically, activities that perform destructive actions like factory resets or significant state changes should be protected by signature-level permissions or require explicit user authentication via biometrics or PIN entry before execution. The absence of these safeguards means that any other installed application on the device can broadcast an intent targeting this specific activity and force it to execute its reset logic. This bypasses standard Android security boundaries, effectively allowing a low-privileged malicious app to interact with high-privilege system functions through misconfigured component exports. Such behavior is characteristic of CWE-284 Improper Access Control vulnerabilities, where the application fails to enforce appropriate restrictions on how components are accessed by other entities within the same device ecosystem.
The operational impact of this vulnerability is severe and directly impacts the availability and reliability of the firewall service. By forcing an arbitrary device reset or triggering a Denial of Service condition through repeated intent broadcasts, an attacker can effectively neutralize the network protection provided by NetGuard. This leaves the Android device exposed to unauthorized network access, data exfiltration, and other malicious activities that the firewall was designed to block. Furthermore, if the reset action clears critical security logs or configuration rules, it may also hinder forensic analysis after a compromise. For enterprise environments or users relying on strict network segmentation, this loss of control over connectivity settings can lead to significant operational downtime and increased risk of lateral movement by threat actors who have gained initial access through other means.
This vulnerability aligns with several entries in the MITRE ATT&CK framework for mobile platforms. It reflects techniques related to Defense Evasion, specifically where an attacker disables or interferes with security tools to avoid detection. Additionally, it relates to Impact tactics involving Denial of Service and Data Manipulation, as the reset action alters the state of the system and removes protective barriers. The ability to force a reset without authorization also touches upon Privilege Escalation concepts in a broader sense, as it allows lower-privileged processes to execute actions reserved for administrators or trusted users. Understanding these mappings is crucial for security teams assessing the risk profile of mobile applications that manage critical infrastructure settings.
To mitigate this vulnerability, developers must immediately implement strict access controls on the ActivityMain component and any other activities responsible for destructive operations. This involves declaring custom permissions in the AndroidManifest.xml file with protectionLevel set to signature or dangerous, ensuring that only apps signed by the same certificate or explicitly authorized users can invoke these actions. Additionally, integrating multi-factor authentication mechanisms before executing reset commands would add a necessary layer of verification. For end-users, until an updated version is released, it is advisable to avoid installing untrusted applications on devices running this vulnerable version of NetGuard and to regularly monitor for official patches from Marcel Bokhorst that address these permission misconfigurations. Regular security audits of Android application manifests are essential to prevent similar access control failures in future updates.