Curl NSS / SSL error after update

Question

I use a custom internal authentication server. With the last round of updates it started having issues, apparently due to a change in the ciphers. This is on a CentOS6 box, fully updated.

curl https://crowd.test.org:8443 \
   --cacert /etc/pki/ca-trust/source/anchors/ca.crt \
   -vvv
* About to connect() to crowd.test.org port 8443 (#0)
*   Trying 192.XXX.XXX.XXX... connected
* Connected to crowd.test.org (192.XXX.XXX.XXX) port 8443 (#0)
* Initializing NSS with certpath: sql:/etc/pki/nssdb
*   CAfile: /etc/pki/ca-trust/source/anchors/ca.crt
  CApath: none
* NSS error -12173
* Closing connection #0
* SSL connect error
curl: (35) SSL connect error
You have mail in /var/mail/root

I checked with nmap and found a supported cipher, TLS_DHE_RSA_WITH_AES_128_CBC_SHA. Checked this on the curl site and found the following does indeed work.

curl https://crowd.mydomain.org:8443 --cacert \
  /etc/pki/ca-trust/source/anchors/ca2.crt \
  -vvv --tlsv1.0 --ciphers rsa_aes_128_sha

How do I correct this? I already used the downgrade method I'd traditionally use without success.

yum history 
yum history undo 106 

Answer 1

Based on https://mozilla.github.io/python-nss-docs/nss.error-module.html it looks like that's a sign that the server has a weak ephemeral Diffie-Hellman key:

SSL_ERROR_WEAK_SERVER_EPHEMERAL_DH_KEY = -12173

On the servers I've seen this error, that was indeed the case.