files

3 Articles

Where Old Files Go To Die

July 26, 2023 by 30 Comments

We all lead digital lives, and we work in and on files of one sort or another. And sometimes we get attached to them. That long manifesto you poured your heart into, but nonetheless probably shouldn’t see the light of day? Love letters from former flames? Your first favorite video game that you can’t play any more, but it just sits there eating up drive space?

These are the files that are important enough that they deserve better than just a drag-and-drop into the trashcan. They deserve to be buried with dignity, and that’s just what [Ulf Schleth]’s /death/null offers us – a digital graveyard where our files no longer exist as they were, but still are allowed to linger in memory.

This is an old project, but one that tickled our funny  and poignant bones in equal parts. The pun on /dev/null probably works just a little better if you read both filepaths with a German accent in your head, but the idea translates anyway.

To use it, you simply upload your file and it gets sent to the great trashcan in the sky, but along the way a 4 x 5 matrix of colored blocks is created that represents the file, and it is registered forever in the graveyard, where you can check up on it any time you like. Of course you can’t read it – only 20 RGB triples remain – but you have the digital “gravestone” as commemoration.

Even if you don’t have any loved ones in [Ulf]’s graveyard, you can walk by and see which files others have chosen to remember. Swing on by and pay your respects to notepad.exe.

File Systems For Tiny Devices

December 7, 2019 by 11 Comments

Sometimes you build a computer and use it every day. Sometimes you build a different type of computer and it sits alone on a mountaintop for years. The design considerations for these two setups are remarkably different, right down to the type of file system used. For small computers like [Jo] is using, and for the amount of time they sit alone in remote locations, he decided to build his own file system for them.

Known as JesFs ([Jo]’s embedded serial File system), the file system is for SPI Flash and intended for use in scientific data logging. It can be used on the chip-scale processors found in many development boards, and is robust enough to use in applications where remoteness is a concern. It has a small RAM footprint, is completely open source, includes wear leveling, and has a number of security features built-in as well.

Some of the benefits of using a file system on such a tiny chip aren’t immediately obvious unless you’re doing a lot of data logging, but it does allow you to change virtually any aspect of the firmware much more easily if everything is accessible as a file, and not something you would have to change by reflashing the whole chip, for example. There are also a number of traps that you can easily fall into when working with file systems for tiny devices.

Screensaver Hack

Bypassing The Windows Lock Screen

February 28, 2015 by 87 Comments

Most of us know that we should lock our computers when we step away from them. This will prevent any unauthorized users from gaining access to our files. Most companies have some sort of policy in regards to this, and many even automatically lock the screen after a set amount of time with no activity. In some cases, the computers are configured to lock and display a screen saver. In these cases, it may be possible for a local attacker to bypass the lock screen.

[Adrian] explains that the screen saver is configured via a registry key. The key contains the path to a .scr file, which will be played by the Adobe Flash Player when the screen saver is activated. When the victim locks their screen and steps away from the computer, an attacker can swoop in and defeat the lock screen with a few mouse clicks.

First the attacker will right-click anywhere on the screen. This opens a small menu. The attacker can then choose the “Global settings” menu option. From there, the attacker will click on “Advanced – Trusted Location Settings – Add – Add File”. This opens up the standard windows “Open” dialog that allows you to choose a file. All that is required at this point is to right-click on any folder and choose “Open in a new window”. This causes the folder to be opened in a normal Windows Explorer window, and from there it’s game over. This window can be used to open files and execute programs, all while the screen is still locked.

[Adrian] explains that the only remediation method he knows of is to modify the code in the .swf file to disable the right-click menu. The only other option is to completely disable the flash screen saver. This may be the safest option since the screen saver is most likely unnecessary.

Update: Thanks [Ryan] for pointing out some mistakes in our post. This exploit specifically targets screensavers that are flash-based, compiled into a .exe file, and then renamed with the .scr extension. The OP mentions these are most often used in corporate environments. The exploit doesn’t exist in the stock screensaver.