nfnl_osf

nfnl_osf [options]

-a
    Add a new OSF signature rule.

-d
    Delete an existing OSF signature rule.

-l
    List all OSF signature rules.

-q
    Query the OSF database with the provided packet data (typically a hex string representation of the packet).

-v
    Verbose output.

-h
    Display help message.

The `nfnl_osf` command is a userspace utility in Linux used to query and interact with the Netfilter OSF (Operating System Fingerprinting) module. This module, part of the Netfilter framework, attempts to identify the operating system of a remote host based on the characteristics of network packets. `nfnl_osf` allows users to list signatures, query the OSF database for a specific packet, add or delete rules, and manage the OSF fingerprinting process. It typically relies on information collected by iptables (or nftables) rules that pass traffic through the OSF module. The command retrieves fingerprint matches based on defined rules and signatures and provides output based on what OSF was able to detect. This helps in tasks such as network security monitoring, intrusion detection, and traffic analysis by providing insight into the devices communicating on the network.

Note that `nfnl_osf` relies on the presence and configuration of the Netfilter OSF module within the Linux kernel. Therefore, its availability and functionality are dependent on the specific kernel version and installed kernel modules.

The `nfnl_osf` command requires root privileges to modify OSF rules. The Netfilter OSF module must be loaded and configured for `nfnl_osf` to function correctly. Syntax and options may vary slightly depending on the kernel version and OSF module version.

Example 1: List all existing OSF rules: nfnl_osf -l
Example 2: Query the OSF database with a sample packet: nfnl_osf -q 00010203040506070809

The `nfnl_osf` command is part of the Netfilter OSF project. It was developed to provide a userspace interface for managing and querying the operating system fingerprinting capabilities of the Netfilter framework. It allows users to add, delete, list and query rules in the Netfilter OSF module.

iptables(8), nft(8), netfilter(7)