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To set up UFW on Debian 12, install the package, allow any required remote-management or service ports, choose your default traffic policies, and only then enable the firewall. If you are connected over SSH, allow the server’s actual SSH port before enabling UFW to reduce the risk of locking yourself out.
What UFW does on Debian 12
UFW, or Uncomplicated Firewall, is a command-line frontend for managing Netfilter firewall rules. Debian’s Bookworm archive lists the ufw package as version 0.36.2-1 in the archive checked on October 8, 2026; package versions can change. Installing it does not activate the firewall or create an active ruleset, as the Debian UFW Wiki explains.
This procedure configures the firewall on the Debian host itself. It does not configure a cloud-provider firewall, router, or upstream network access control; check those separately if your server uses them.
Install UFW and inspect its current state
Update APT’s package index, install UFW, and check whether it is already active before changing rules:
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sudo apt update
sudo apt install ufw
sudo ufw status verboseThe status command reports whether UFW is active and, when available, its default policies and UFW-managed rules. If UFW is already active, inspect its rules before modifying them so you do not unintentionally disrupt existing access.
Allow remote SSH access before enabling the firewall
If you administer the machine over SSH, identify the port the SSH service actually listens on. Do not assume it is port 22 if the host has been customized. Allow the correct access before enabling UFW: the Debian Wiki warns that enabling the firewall can interrupt existing connections, and the UFW manual documents adding the SSH rule before activation.
Use an installed application profile
List available profiles and inspect a profile’s ports with:
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sudo ufw app list
sudo ufw app info OpenSSHIf an OpenSSH profile is installed and matches your SSH configuration, allow it:
sudo ufw allow OpenSSHProfile availability depends on the packages installed on the system. The UFW manual documents the ufw app list and ufw app info commands; the Bookworm package file list also records UFW’s profile-related files.
Allow a specific SSH port instead
If there is no matching profile, or SSH listens on a different port, allow that port and protocol explicitly. For standard SSH on port 22:
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sudo ufw allow 22/tcpReplace 22 with the actual listening port when necessary. Where practical, open a second SSH session to test access before closing the session you used to configure the firewall. Do not use ufw --force enable as the routine method; enabling normally prompts when UFW detects SSH use.
Set default policies and allow only needed services
Choose policies that fit the host’s role. A common server baseline denies unsolicited incoming connections and allows outbound connections, then adds explicit exceptions for services the server must provide:
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sudo ufw default allow outgoing
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sudo ufw allow 443/tcp # only if this host serves HTTPSPorts 80 and 443 are examples, not requirements. Add rules only for services that are running and need to be reachable. UFW supports rules by port and protocol; for application-specific syntax and options, consult the Debian UFW manual.
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Generic rules such as ufw allow 22 apply to IPv4 and IPv6 when IPv6 support is enabled in UFW. Its IPV6 setting is in /etc/default/ufw, and the manual says IPv6 is enabled by default in the UFW configuration. Check that the intended rules cover the address families your host uses rather than disabling IPv6 firewalling without a deliberate reason.
Enable UFW and verify the result
After adding the required access rules and setting the policies, enable UFW:
sudo ufw enableEnabling UFW loads the firewall rules and enables the firewall at boot. Then review the status and numbered rules:
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sudo ufw status verbose
sudo ufw status numberedConfirm that the firewall is active, the displayed default policies are the ones you intended, and required services appear in the rules. Numbered output is useful when you later need to identify a UFW-managed rule for deletion.
Understand what UFW status does not show
ufw status displays rules managed through UFW’s command interface; it is not a complete view of every rule that may be loaded from configuration files or other firewall tools. For a broader view of the running filter tables, the UFW manual documents:
sudo ufw show rawUFW’s command interface is designed for straightforward rule management, not every possible Netfilter configuration. Debian’s Handbook section on firewalls and packet filtering discusses UFW in the wider context of Netfilter tooling. More complex configurations may use files under /etc/ufw/.
Optional: turn on firewall logging
Enable UFW’s default low-level logging with:
sudo ufw logging onThe documented levels are off, low, medium, high, and full. Higher levels can generate substantial output; the UFW manual warns that levels above medium may fill a disk quickly. Choose a level appropriate to your monitoring and storage needs.
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