Mfcttrf

Imagine the following code:

ATTACKERDATA="$(cat attackerControlledFile.txt)"
echo "$ATTACKERDATA"

An attacker can, through whatever arbitrary process, modify the contents of attackerControlledFile.txt to anything they desire. The content can be ASCII, UTF-8, Binary, etc. Anything is fine. The machine also assumes that it is infinitely fast, so even an extremely large file of multiple terrabytes would be read and printed immediately.

Is it possible for an attacker, regardless of how unlikely it would be, to exploit this somehow by modifying the content of attackerControlledFile.txt? "Somehow" refers to things like:

• This code only works in bash
  


• This code requires the output to be printed onto a specific terminal emulator


• Etc.

Everything else assumes a reasonably sane system. This means that answers such as "If echo is an attacker-controlled binary that's actually malware" does not count, as the existence of malware is not exactly "reasonably sane". Answers that would require a specific software or version of that software to be present do count, as long as that software was not made for the purpose of exploitation.

A similar question asks Is it possible to use the Linux “echo” command maliciously?, but the accepted answer is actually about a flaw in the design of a web application. Furthermore, it requires the attacker to be able to do redirects, which as far as I know, this construct cannot do.

Is it possible for an attacker, regardless of how unlikely it would be, to exploit this somehow by modifying the content of attackerControlledFile.txt? "Somehow" refers to things like:

This code requires the output to be printed onto a specific terminal emulator

In fact, yes. Old terminals like vt100 have the ability to use ANSI escape sequences to do special things, like execute commands. The following site below documents this ability using a simple echo, like you describe.

https://www.proteansec.com/linux/blast-past-executing-code-terminal-emulators-via-escape-sequences/

The article is in depth with specific exploit instructions, but the general idea can be summarized from this excerpt from the site:

Dangerous Escape Sequences
Terminal emulators support multiple features as described below [8]:

• Screen Dumping: a screen dump escape sequence will open arbitrary file and write the current content of the terminal into the file. Some terminal emulators will not write to existing files, but only to new files, while others will simply overwrite the file with the new contents. An attacker might use this feature to create a new backdoor PHP file in the DocumentRoot of the web server, which can later be used to execute arbitrary commands.




• Window Title: an escape sequence exists for setting the window title, which will change the window title string. This feature can be used together with another escape sequence, which reads the current window title and prints it to the current command line. Since a carriage return character is prohibited in the window title, an attacker can store the command in a window title and print it to the current command line, but it would still require a user to press enter in order to execute it. There are techniques for making the command invisible, like setting the text color to the same color as the background, which increases the changes of user pressing the enter key.




• Command Execution: some terminal emulators could even allow execution of the command directly by using an escape sequence.

No, echo used in the example above is fine

Echo simply prints a string to the pipe stdout (default)

per: https://superuser.com/a/699500/527937

Pipes can't overflow. A pipe is just a buffer (a certain amount of
memory, most likely 64KB on a current system) between a producer and a
consumer. If the producer produces faster than the consumer consumes,
the producer is blocked (that means, the program will sleep) until the
consumer makes room in the buffer again by reading from it.

As a side note, if you have a large ammount of data in 1x line ... cat can hang and/or consume an enormous amount of system memory.

Does

echo "$(cat /etc/shadow)"

or

echo "$(mv test.txt test2.txt)"

Satisfy your requirement?