Exam PT0-001 topic 1 question 153 discussion

Actual exam question from CompTIA's PT0-001

Question #: 153
Topic #: 1

A penetration tester is attempting to open a socket in a bash script but receives errors when running it. The current state of the relevant line in the script is as follows:

Which of the following lines of code would correct the issue upon substitution?

A. open 0<>/dev/tcp/${HOST}:${PORT}
B. exec 0</dev/tcp/${HOST}/${PORT}
C. exec 0</dev/tcp/$[HOST]:$[PORT]
D. exec 3<>/dev/tcp/${HOST}/${PORT}
E. open 3</dev/tcp/${HOST}/${PORT}
F. open 3</dev/tcp/$[HOST]/$[PORT]

Show Suggested Answer

Suggested Answer: C 🗳️

by Matherson at May 2, 2021, 3:50 p.m.

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Matherson

Highly Voted 4 years, 2 months ago

$ exec {file-descriptor}<>/dev/{protocol}/{host}/{port} should be the command to open a socket in bash. https://www.xmodulo.com/tcp-udp-socket-bash-shell.html This site breaks down and explains each part of the syntax. I found it super helpful.

upvoted 8 times

Matherson

4 years, 2 months ago

D is the answer. Only one with the correct $exec 3

upvoted 2 times

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macr0sss

Highly Voted 4 years, 2 months ago

answer D. file descriptor needs to be over 2 (so 3 is ok), read/write <> and rest same everywhere.

upvoted 6 times

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miabe

Most Recent 3 years ago

Selected Answer: D

looks good to me

upvoted 1 times

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Moytra

3 years, 8 months ago

Fyi, definitely this is the D one. After some research everything points that we can focus in the sistaxis itself, so the File descriptor reserved in bash are the 0,1,2 Saying that we have remaining D E F, However, to open a socket is with exec. And the sistaxis correct says that is $ exec {file-descriptor}<>/dev/{protocol}/{host}/{port} Take a look in the <> D is the only one that has the correct one, this is definetely D.

upvoted 1 times

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MonKEY69

4 years ago

I would put D. https://unix.stackexchange.com/questions/336876/simple-shell-script-to-send-socket-message

upvoted 1 times

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Lekitchen

4 years, 2 months ago

I would think that the correct answer would be D. The syntax for C includes $[HOST]:$[PORT], doesn't match the syntax found on https://www.xmodulo.com/tcp-udp-socket-bash-shell.html. My reasoning for D being correct is that in order to use the shell as an exploit, you would want it to be both readable and writable. So you would need a <> to be present.

upvoted 1 times

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