MediumOS hardeningBLWK-KERNEL-014

ICMP redirects are accepted

What this means

net.ipv4.conf.all.accept_redirects is 1 — this host will update its routing table based on unauthenticated ICMP redirect packets from anyone on the local network, a classic man-in-the-middle primitive for redirecting traffic through an attacker-controlled host.

How to fix it

Set net.ipv4.conf.all.accept_redirects=0 via /etc/sysctl.d/ and run sysctl --system.

Check it yourself

Run a scan and look for BLWK-KERNEL-014 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:

accept_redirects == 1

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

References

• CIS Benchmark 3.2.1
• MITRE ATT&CK T1557

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