picoCTF Writeup picoGym Practice Challenges Static ain't always noise (注意<spoiler>)

Description

Can you look at the data in this binary: static? This BASH script might help!

二つのファイルが渡される。(.bash,bainary)
とりあえず二つとも実行してみる

ltdis.sh

#!/bin/bash



echo "Attempting disassembly of $1 ..."


#This usage of "objdump" disassembles all (-D) of the first file given by 
#invoker, but only prints out the ".text" section (-j .text) (only section
#that matters in almost any compiled program...

objdump -Dj .text $1 > $1.ltdis.x86_64.txt


#Check that $1.ltdis.x86_64.txt is non-empty
#Continue if it is, otherwise print error and eject

if [ -s "$1.ltdis.x86_64.txt" ]
then
	echo "Disassembly successful! Available at: $1.ltdis.x86_64.txt"

	echo "Ripping strings from binary with file offsets..."
	strings -a -t x $1 > $1.ltdis.strings.txt
	echo "Any strings found in $1 have been written to $1.ltdis.strings.txt with file offset"



else
	echo "Disassembly failed!"
	echo "Usage: ltdis.sh <program-file>"
	echo "Bye!"
fi

>bash ltdis.sh       
Attempting disassembly of  ...
Disassembly successful! Available at: .ltdis.x86_64.txt
Ripping strings from binary with file offsets...

staticをとりあえずa.outとコピーし実行すると

$ ./a.out
Oh hai! Wait what? A flag? Yes, it's around here somewhere!

実行結果からみてbashファイルにstaticを読み込ませれば良さそう。

$ bash ltdis.sh static
Attempting disassembly of static ...
Disassembly successful! Available at: static.ltdis.x86_64.txt
Ripping strings from binary with file offsets...
Any strings found in static have been written to static.ltdis.strings.txt with file offset

出力されたstatic.ltdis.x86_64.txtを見てみるとフラグが書かれている。

picoCTF{d15a5m_t34s3r_1e6a7731}