IT Forensics · Linux

Forensic analysis of iptables/nftables rules – checking firewall configuration and whether it has been tampered with

On Linux, iptables and the more modern nftables control packet-based filtering of network traffic. Their sets of rules determine which traffic is allowed, blocked or forwarded.

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A rule that has been specifically inserted can be used to permanently allow additional, unauthorised network access or to bypass certain monitoring mechanisms; this is why firewall rule sets are subject to forensic analysis.

Why LanCologne?

Since its foundation, LanCologne has specialised in professional IT forensics. Our staff have decades of experience in the field of information technology and assist companies, solicitors, private individuals and, on a regular basis, the courts in the technical investigation of complex digital matters.

The examination is, as a matter of principle, carried out exclusively on a forensic copy, a forensic image or a data source captured in a technically equivalent manner that preserves the integrity of the evidence. The original evidence remains unchanged and is stored in a manner that preserves its integrity.

Our services

We carry out a comprehensive analysis of the active and persistent firewall configuration, check individual rules for anomalies, and link any unusual permissions to potential persistence or exfiltration mechanisms.

Typical areas of application

•Detection of additional, unauthorised firewall exceptions
•Investigation of deactivated security rules
•Analysis of port forwarding and NAT configurations
•Assessment of a system’s network exposure
•Incident Response on Linux Systems
•Judicial and non-judicial expert reports

This is how an iptables/nftables analysis works

Once the system has been backed up, both the currently active firewall configuration and the persistent configuration loaded at system start-up are recorded. Each rule is checked for plausibility and compared with expected standard configurations. Any unusual permissions or forwarding rules are documented separately.

Why is firewall analysis relevant to forensic investigations?

An unauthorised firewall rule can allow an attacker to gain persistent network access, even if other persistence mechanisms have been detected and removed.

The deliberate deactivation of existing protection rules can also be a key part of an attack sequence and is therefore scrutinised just as carefully as newly added rules.

Frequently Asked Questions

What is the difference between iptables and nftables?+
nftables is the more modern successor to iptables, featuring a standardised syntax and, in some respects, enhanced functionality; however, both serve the same basic purpose of packet filtering.
How can a tampered firewall rule be detected?+
By comparing against known, expected configurations and checking for unusual permissions, forwarding rules or disabled protection rules.
Are temporary, non-persistent rules also recorded?+
In the case of live monitoring of a running system, yes; in the case of a purely offline analysis, only the persisted configuration.

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