UMassCTF '21 Hermit 2 WriteUp
March 28, 2021
The image above is what we see when visiting the challenge URL (
That’s strange. Initially I thought the site is down but it’s fine.
Let’s try to connect with NetCat and see what the server tell us and why browser can’t display it.
nc -vvv 188.8.131.52 8087
and response we get back is:
184.108.40.206.bc.googleusercontent.com [220.127.116.11] 8087 (?) open SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u2
Doesn’t look like valid HTTP resopnse lol. Ok now we know that SSH server is running on that port so let’s try to connect.
ssh 18.104.22.168 -p 8087 - and we see the prompt to enter a password for myself (krydos). It isn’t clear what user should I use.
And even if we know the user what is the password?
As a hint the challenge name is
hermit so the user is probably has the same name but we still need to know password.
Poking around, trying different things I noticed that hermit 2 challenge is on the same IP address where hermit 1 is.
That’s actually great because we have shell access on the server from the previous challenge.
So I went to
/home/hermit/.ssh folder, copied user’s private key and used it in my ssh command like this:
ssh -i /tmp/hermit.ssh.private.key email@example.com -p 8087
We’re in. Now… where is the flag? We know one flag from the previous challenge but I wasn’t able to find another one.
Grep’ing everything didn’t help.
My assumption was that the flag is somewhere in
/root folder or somewhere else where hermit user doesn’t have access to.
Now… how can I become a root? Tried some stuff but didn’t find anything useful.
Then I grepped for
/etc folder and I found
hermit ALL = (root) NOPASSWD: /bin/gzip -f /root/rootflag.txt -t in
This record means that we can execute that command without asking for password.
Let’s do it:
sudo /bin/gzip -f /root/rootflag.txt -t and we see the flag -
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