Occasionally report error from my running application server

[niujh]

Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. crt.sh | example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.

My domain is:hqyc1973.com

It produced this output:[26/Apr/2021:10:07:36] ENGINE Error in HTTPServer.tick
Traceback (most recent call last):
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/server.py", line 1776, in serve
self.tick()
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/server.py", line 1999, in tick
conn = self.connections.get_conn(self.socket)
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/connections.py", line 180, in get_conn
return self._from_server_socket(server_socket)
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/connections.py", line 199, in _from_server_socket
s, ssl_env = self.server.ssl_adapter.wrap(s)
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/ssl/builtin.py", line 244, in wrap
sock, do_handshake_on_connect=True, server_side=True,
File "/usr/lib/python3.6/ssl.py", line 407, in wrap_socket
_context=self, _session=session)
File "/usr/lib/python3.6/ssl.py", line 817, in init
self.do_handshake()
File "/usr/lib/python3.6/ssl.py", line 1077, in do_handshake
self._sslobj.do_handshake()
File "/usr/lib/python3.6/ssl.py", line 689, in do_handshake
self._sslobj.do_handshake()
ssl.SSLError: [SSL: BAD_DH_G_LENGTH] bad key share (_ssl.c:852)

2021-04-26 10:07:36 AM HTTPServer Thread-3 140035224721152 [26/Apr/2021:10:07:36] ENGINE Error in HTTPServer.tick
Traceback (most recent call last):
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/server.py", line 1776, in serve
self.tick()
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/server.py", line 1999, in tick
conn = self.connections.get_conn(self.socket)
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/connections.py", line 180, in get_conn
return self._from_server_socket(server_socket)
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/connections.py", line 199, in _from_server_socket
s, ssl_env = self.server.ssl_adapter.wrap(s)
File "/home/ubuntu/.local/lib/python3.6/site-packages/cheroot/ssl/builtin.py", line 244, in wrap
sock, do_handshake_on_connect=True, server_side=True,
File "/usr/lib/python3.6/ssl.py", line 407, in wrap_socket
_context=self, _session=session)
File "/usr/lib/python3.6/ssl.py", line 817, in init
self.do_handshake()
File "/usr/lib/python3.6/ssl.py", line 1077, in do_handshake
self._sslobj.do_handshake()
File "/usr/lib/python3.6/ssl.py", line 689, in do_handshake
self._sslobj.do_handshake()
ssl.SSLError: [SSL: BAD_DH_G_LENGTH] bad key share (_ssl.c:852)

My web server is (include version): Cherrypy

The operating system my web server runs on is (include version):Ubuntu 18.04 LTS

My hosting provider, if applicable, is: AWS route 53

I can login to a root shell on my machine (yes or no, or I don't know): yes

I'm using a control panel to manage my site (no, or provide the name and version of the control panel):

The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot): certbot 1.14.0

[Osiris]

Could you please give us more context?

Yesterday, your site was working perfectly on HTTPS.. What changed?

[niujh]

Sure.

I just left my website server running for the night, didn't change any settings. This morning when I read through the logs I found so many errors. Could it be due to my settings?

Here is my server settings in Cherrypy:
"global": {
'server.socket_host':
'0.0.0.0',
'server.socket_port':
443,
'server.ssl_module':
'builtin',
'server.ssl_certificate':
os.path.join(ROOT_ABSOLUTE_PATH, "cert.pem"),
'server.ssl_private_key':
os.path.join(ROOT_ABSOLUTE_PATH, "privkey.pem"),
'server.ssl_certificate_chain':
os.path.join(ROOT_ABSOLUTE_PATH, "chain.pem")
},

[Osiris]

Seems to be an issue with DH key exchange. If I only advertise DHE cipher suites using openssl, I can't connect:

openssl s_client -connect hqyc1973.com:443 -tls1_2 -cipher DH
CONNECTED(00000003)
140576096184128:error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure:ssl/record/rec_layer_s3.c:1543:SSL alert number 40
(...)

But your webserver still works using ECDHE and conventional RSA. Note that conventional RSA key exchange is not recommended due to lack of forward secrecy.

[niujh]

This is some food for thought, I'll do more research on this RSA stuff. Is it safe just for now to continue running my server and ignore this error report?

[Osiris]

@niujh

Is it safe just for now to continue running my server and ignore this error report?

I believe it is. The DH (Diffie-Hellman) key exchange protocol is rather CPU-heavy and there's a fine fast and safe alternative ECDH(E) ([Ephemeral] Elliptic Key Diffie-Hellman) which is working nicely on your server, so if you'd ask me: not really a big problem.

Some ancient clients don't have ECDHE capabilities, but the plain old RSA key exchange (which isn't very good) can fill that gap. DHE (Ephemeral Diffie-Hellman), which does have forward secrecy, is an alternative for older clients and have forward secrecy, but I'm guessing not many clients fall into that category.

[niujh]

Thanks. By the way, I tried replacing "chain.pem" with "fullchain.pem" in my settings and the server just work exactly fine! Is it safe to just use "fullcian.pem" here?

[Osiris]

Not sure, depends on how CherryPy handles the certs. If you also specified chain.pem already, it's not very usefull to change cert.pem to fullchain.pem.

If CherryPy handles the certs in a dumb/unusual way, it might unnecessary increase the TLS handshake by adding the intermediate certificate twice.