Forensic Blogs

An aggregator for digital forensics blogs

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Quickpost: finger.exe

Windows 10 comes with the finger command, an ancient computer network tool.

You can still use it to lookup weather information, for example 🙂

It establishes a TCP connection to the hostname/IP address after the @ character, using destination port 79. And then it sends the text before the @ characters in ASCII, terminated with carriage return & line feed.

After that, it reads the reply, displays it, and closes the TCP connection.

finger.exe is not proxy-aware.

Port 79 is not hardcoded as an integer in finger.exe: the port is identified by service name “finger” (UNICODE), which is defined in the services list (%SystemRoot%\system32\drivers\etc\services). GetAddrInfo uses this list.

If you replace “finger” with “http\x00\x00” (UNICODE) in finger.exe (via binary patching, a shim, …), the finger command will connect to port 80:

As noted by many, finger.exe can be (ab)used to exchange information and files. Here I had my own go at it with finger.exe & Excel:

 

Quickpost info

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Quickpost: Portable Power

I did some tests to generate electricity (230V AC) with a portable 12V battery (well, it’s 10 Kg).

I have a 12V VRLA battery with a capacity of 35,000 mAh. That’s 12V times 35 Ah = 420 Wh. Or equivalent to a 116,667 mAh (420,000 mWh / 3.6 V) USB powerbank.

Charging this 12V battery with a 12V battery charger connected to a 230V power outlet takes almost 7 hours (6:57) and requires 0.49 kWh. That is measured with a plug-in electricity meter with a .00 kWh precision. And I’m working under the assumption that the power requirement of the electricity meter is so small that it can be neglected.

Then I use this fully charged battery to power a 230V 150W halogen lamp via a 12V DC to 230V AC power inverter (modified sine wave).

It runs for 2 hours (2 tests: 2:01 and 2:03) and consumes 0.30 kWh.

Of the 0.49 kWh energy I put into my system, I get 0.30 kWh out of the system. That’s 61%, or a bit better than half of the energy I put into the system.

The main phases where I expect the energy losses are occurring, is in 230V AC to 12V DC conversion and electrical to chemical energy conversion (charging); and chemical to electrical conversion and 12V DC to 230V AC conversion (discharging). I believe the highest energy loss to occur in the power inverter.

And with energy loss, I mean energy that is converted into forms that are not directly useful to me, like heat.

Remark that the halogen lamp test stopped after 2 hours, because the power inverter stopped converting. The battery voltage was 11.5 V then, and I could still draw 1 A at 11.5 V for an hour (I stopped that test after 1 hour).

Next I’m going to try out a 12V to 5V adapter and power some USB devices.

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Quickpost: VMware OS Version Snapshots

Whenever I upgrade the operating system of my virtual machines, I take a snaphot right after the upgrade.

This gives me a tree of different OS versions:

I give each snapshot a small descriptive name, that starts with the date of the snapshot (YYYYMMDD).

This allows me to revert to older versions to experiment with patched vulnerabilities, like this one.

Quickpost info