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How the Mentioned CVE Works
The vulnerability stems from a logic error in netfoil’s optional seccomp sandboxing feature. The `–filter-system-calls` flag, intended to apply additional system call filters after the binary has started, fails to activate even when explicitly specified. The flawed implementation causes the enforcement of sandboxing rules to be completely skipped, leaving the process running without the expected seccomp confinement.
Because the security is a defense-in-depth measure, its absence does not directly trigger a panic or error; the binary continues to execute normally. An attacker who can influence netfoil’s execution environment may exploit this missing filter to invoke otherwise restricted system calls. In a containerised or systemd‑managed deployment, the missing filter removes a critical layer of protection that would have limited the process’s access to the kernel.
This bypass is particularly concerning when netfoil is paired with a systemd service that disables primary sandboxing and relies solely on netfoil’s own seccomp filters. The example configuration shipped with netfoil expects the `–filter-system-calls` flag to be effective, but in vulnerable versions it provides no restriction. The issue is fixed in netfoil v0.2.1, where the flag logic is corrected and seccomp filters are reliably applied.
DailyCVE Form
Platform: netfoil
Version: < 0.2.1
Vulnerability: seccomp bypass
Severity: Moderate
Date: 2026-04-29
Prediction: 2026-05-06
What Undercode Say
Check netfoil version netfoil --version Verify whether the --filter-system-calls flag is working (vulnerable if no seccomp appears in strace output) strace -e seccomp netfoil --filter-system-calls For Go‑based netfoil, inspect the seccomp profile loading in the source grep -r "seccomp" $(go env GOMODCACHE)/github.com/tinfoil-factory/netfoil@ Confirm the fix in commit 8c84f1b git clone https://github.com/tinfoil-factory/netfoil cd netfoil git show 8c84f1b
Exploit
No public exploit is available because the missing filter merely reverts to the default, unrestricted system call set. An attacker who already has local access can leverage this flaw to execute system calls that would have been blocked, such as those used for privilege escalation or container escape. The impact is entirely dependent on the environment in which netfoil runs.
Protection
Upgrade to netfoil v0.2.1 or later.
go get github.com/tinfoil-factory/[email protected]
Alternatively, apply a systemd sandboxing directive that does not rely on netfoil’s internal flag:
[bash] SystemCallFilter=~@privileged @resources
Monitor for any use of the `–filter-system-calls` flag in existing deployments and verify that it is enforced by checking seccomp status.
Impact
Reduced sandboxing – The netfoil binary runs without the additional seccomp restrictions it was supposed to impose, weakening the overall security posture of any service that depends on this flag. In containerised environments, the missing filter may allow a compromised netfoil process to perform actions that could otherwise lead to container breakout (e.g., executing a writable file in /dev/shm). For systemd‑managed services, the defense‑in‑depth layer that would have limited kernel access is absent, making it easier for an attacker to elevate privileges from within the service.
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Reported By: github.com
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