MediumOS hardeningBLWK-KERNEL-010

Hardlink creation protection is disabled

What this means

fs.protected_hardlinks is 0 — any user can create a hardlink to a file they don't own (e.g. a setuid binary or a file another process will later run as root), a classic TOCTOU/race primitive for local privilege escalation.

How to fix it

Set fs.protected_hardlinks=1 via /etc/sysctl.d/ and run sysctl --system.

Check it yourself

Run a scan and look for BLWK-KERNEL-010 in the results:

bulwark scan

Installed the standalone CLI package instead of the app? The command is bulwarkctl.

How Bulwark decides

Bulwark reads sysctl_kernel and reports this check when:

protected_hardlinks == 0

If a value can't be read, Bulwark reports the check as undetermined rather than passing it. View the rule source.

References

• CIS Benchmark 1.5.7
• MITRE ATT&CK T1068

Related checks

• Cron entry runs a downloader piped to a shell · BLWK-ACCT-001
• Password maximum age is excessively long · BLWK-ACCT-002
• Password minimum age is zero · BLWK-ACCT-003
• Password hashing rounds are not explicitly configured · BLWK-ACCT-004
• Default UMASK is not explicitly configured · BLWK-ACCT-005
• A sensitive system file is world-writable · BLWK-FS-001