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Renewing the Thecus N7510’s TLS certificate

The Thecus N7510 is a cheap NAS that used to be popular for its large amount of disks (7) while still being as cheap as (or even cheaper than) most 4-disks NAS.

It is powered by Thecus OS, but sadly it seems that its version of Thecus OS isn’t maintained very actively anymore. Particularly, the SSL/TLS certificate used for FTP over TLS expired about a month ago. Which is pretty annoying, because FileZilla refuses to let you permanently ignore a certificate expiration alert (for stupid reasons, but this isn’t the first time the FileZilla developers provide poor explanations for equally poor choices – we can only live with that).

So the only option I had left was to try to upgrade the NAS’s certificate by myself. Gladly, this turned out fairly easy, as I wrote a guide before on how to create your own self-signed certificate. So the only new (and minor) difficulty was to find where the current SSL/TLS certificate of the N7510 is. I quickly found that it’s named /etc/ssl/private/pure-ftpd.pem, which contains both the server private key and the signed certificate (something very slightly different from my previous guide: you just need to stash 2 files into one .pem file).

If they’re not already enabled, you need to enable SSH and SFTP from the ThecusOS control panel (the SSH & SFTP toggles are in Network Service > SSH)

Once this is done, here are the commands I used (cf the linked guide if you need more details) to generate the certificate:

cd /etc/ssl/private
openssl genrsa -des3 -out servPriv.key 4096
openssl req -new -key servPriv.key -out servRequest.csr
cp servPriv.key servPriv.key-passwd
openssl rsa -in servPriv.key-passwd -out servPriv.key
openssl x509 -req -days 365 -in servRequest.csr -signkey servPriv.key -out signedStartSSL.crt

At this stage, you have everything you need excepted the “stashed” pem file.
At first, I tried to use nano to create it, but the Thecus N7510 doesn’t have nano 😡 So, I connected via SFTP (with FileZilla) as root (that’s why I told you to enable SFTP along with SSH earlier). Then I grabbed servPriv.key and signedStartSSL.crt, and put them both into a single text file (not sure if the order matters) name newcert.pem.

Just for the sake of clarity, newcert.pem looks like:

-----BEGIN RSA PRIVATE KEY-----
[base64 stuff]
-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
[more base64 stuff]
-----END CERTIFICATE-----

Finally, I uploaded newcert.pem into /etc/ssl/private, renamed pure-ftpd.pem to pure-ftpd.pem.bak, and renamed newcert.pem to pure-ftpd.pem.

All is now ready, the last thing you need to do is to restart the FTP server. The easiest way to do it is to disable then re-enable it via the ThecusOS control panel (Network Service > FTP).

Now, when you connect with FileZilla to the FTP server, you’ll see your new, non-expired, certificate, and will be able to trust it permanently (that is, until it expires in about 10 years).

Posted in FTP, security, servers.


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