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Security Advisory: CSF Firewall Port Rule Race Condition

A race condition in ConfigServer Security & Firewall (CSF) port rule handling is fixed in this security release: under concurrent reloads, a port rule could briefly apply incorrectly, exposing management ports at the wrong moment. Reinstall CSF from ConfigServer and restart the firewall.

Low
CSF AlmaLinux 8 AlmaLinux 9 CentOS 7 CloudLinux 7 CloudLinux 8 CloudLinux 9

Affected Versions

CSF 14.20 and earlier

Patched Version

CSF 14.21

Default Update CMD

yum update -y

Fix Commands

AlmaLinux 9 / CloudLinux 9

cd /etc/csf
csf -u
csf -r

AlmaLinux 8 / CloudLinux 8

cd /etc/csf
csf -u
csf -r

CentOS 7 / CloudLinux 7

cd /etc/csf
csf -u
csf -r

What this means under a SharedLicense license

Your SharedLicense license itself is not affected — this is a change in AlmaLinux 8, AlmaLinux 9 software, not in licensing. Update the product through its standard update channel. Licenses keep working through updates; nothing needs re-issuing or re-activating.

What happened

CSF applies its port rules by regenerating and reloading firewall configuration. The race condition meant two overlapping reloads could interleave, leaving a rule in the wrong state — in the worst case, a management port that should be closed stayed open until the next clean reload.

Who is affected

Servers running CSF where rules change automatically (login failures, cluster updates) — the overlap windows are exactly those automatic flows.

How to apply the fix

  • Reinstall CSF from the ConfigServer distribution: csf.tgz, then csf -r to reload rules cleanly.
  • Verify listening ports against csf.conf expectations after the reload.

For SharedLicense customers

Licensing is unaffected — CSF is free firewall software. This is a low-severity fix; apply it in the regular maintenance window.

Frequently Asked Questions

What is the CSF race condition?
Concurrent rule reloads could interleave and leave a port rule briefly in the wrong state.
How do I apply the fix?
Reinstall CSF from the ConfigServer distribution and run csf -r to reload rules cleanly.
How serious is it?
Low — a temporary window, but on management ports; worth patching in the normal cycle.

References

Security Advisories

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