shad0w

Index

1. Problem information

2. Problem solving

3. Review

[Problem information]

[Problem solving]

1. I accessed the server with rcity7 user.

2. There was no "flag" file. So I had to find a running network port as shown in the problem information.

3. I used the "netstat -a" command to check the network connection status, but the "netstat" command doesn't work. Therefore, I scanned the localhost using "nmap", a tool for scanning the network. Of the open ports, port 9999 was suspected.

4. I used "netcat" to access that port, and putted the password. 

[Review]

You could find more description or options about nmap, netcat using "man" command.

1. find / -name "password": Serch for the file name "password" in the entire file system.

2. grep -r "password" /: Serch for the character "password" in the entire file system.

3. ls -IR | grep "password": Displays a list of files in the current directory and subdirectories, filtering and outputting the string "password" from that list.

4. chmod -R 777 / | grep "password": Trying to change permissions for all files and directories while also finding lines containing the string "password".

Index

1. Problem information

2. Problem solving

3. Review

[Problem information]

[Problem solving]

1. I accessed the server with rcity6 user.

2. I listed the files, and there was a "flag" file. The problem information said that I shoud find out what type of this file is. So I used file command to find out what it is. "flag" file was a ELF type file. ELF files are executable files that run on Linux, such EXE files.

3. I tried to check the content of "flag" file using cat command, but the text came out broken.

4. Then I used strings command to print out all strings to the terminal. As a result, I could find the strings similar with flag pattern/lengths.

[Review]

It's quite easy.

Index

1. Problem information

2. Problem solving

3. Review

[Problem information]

[Problem solving]

1. I Accessed the server with rcity5 user.

2. I listed the files, and there was a "flag.txt" file. So I printed the contents of that file to the terminal. There was a string encoded in base64. The base64 incoded string ends with '='. It looked like it would have to be decoded.

3. I used the base64 command to decode that string. 

4. There was another way to decode that text. That is using BASE64 decode web service.

(https://www.base64decode.org/)

[Review]

You can see options for the base64 command in the picture below.

The base64 encoding and decoding methods in the terminal are summarized as follows. 

-Base64 incoding: base64 'file name'

-Base64 decoding: base64 -d 'file name' 

Index

1. Problem information

2. Problem solving

3. Review

[Problem information]

[Problem solving]

1. I Accessed the server with rcity4 user.

2. I listed the files, and there was a "flag.txt" file, so I checked the contents of that file. There were too many strings in it.

3. In the problem information, the flag was said to be near the string "flag is here". First, I tried to find the "flag is here" string in the "flag.txt" file using the grep command. But, there was nothing about that as a result. After that I added the -i option to ignore case distinctions in patterns and data for find the "flag is here" string. A string called "fLag Is HerE" string was derived, and a string presumed to be a flag could be identified next to it.

[Review]

You can see many options for the grep command in the picture below.

Index

1. Problem information

2. Problem solving

3. Review

[Problem information]

[Problem solving]

1. I Accessed the server with rcity3 user.

2. As shown in the problem information, you need to find the "<flag-file>.txt" file among the numerous directories. In fact, there were many directories in the server. 

3. I used the find command to retrieve all files with the ".txt" extension under the current directory. There was only one ".txt" extension files. So I checked the content of the "f14g.txt" file.

[Review]

You can see many options for the find command in the picture below.

Index

1. Problem information

2. Problem solving

3. Review

[Problem information]

[Problem solving]

1. I accessed the server by inserting the contents of the flag file of Operation RCity1 problem with a password.

2. I used the ls command to see which files or directories exist in the current path. There was nothing in it. So I used the -a option to list all files and directories, including hidden files. There were four hidden files.

3. Among hidden files, the ...catthisfile.txt file was very suspicious. That's like saying "Hey check the content of this file usi

ng cat command". Therefore I checked the content of this file. 

[Review]

The ls command has a number of options. You can see a description of the -a option as well. It says, "do not ignore entries starting with .". Most hidden files are files that begin with '.'. That means this option will also include the hidden files.

Index

1. Problem information

2. Problem solving

3. Review

[Problem information]

[Problem solving]

1. I accessed to the server using SSH. But the server required a password. There was a hint about password in problem information. It said "flag.txt file will contain the password". So I put the contents of the flag file obtained from the Operation RCity0 problem as a password.

2. I determined which files or directories exist in the current path. There were three directorys. In particular, there was a directory named flag. I accessed to it, but there was no files in it.

3. Then I checked the directory named 'maybe here'. There was a 'fl ag.txt' file in it. So I checked what was in there. 

[Review]

It's easy.

Index

1. Problem information

2. Problem solving

3. Review

[Problem information]

[Problem solving]

1. Let's access to the server using SSH. The ssh command consists of: ssh Username@Address-p Port 

2. I used the ls command to see which files exist in the current path. There was a file named flag.

3. Then I checked the contents of the flag file through the cat command.

[Review]

So far, I have mainly solved problems accessed through netcat rather than SSH. it was a beneficial time to get used to SSH.