Errno 14 Invalid file descriptor

Hi there!
Since yesterday, our red hat servers can't connect ot the red hat repos anymore. When trying to exec "yum repolist enabled" on a RH 7.5, the output was:

Loaded plugins: aliases, changelog, etckeeper, kabi, langpacks, product-id, search-disabled-repos, subscription-manager, tmprepo, verify, versionlock
Loading support for Red Hat kernel ABI
https://cdn.redhat.com/content/dist/rhel/server/7/7Server/x86_64/os/repodata/repomd.xml: [Errno 14] curl#35 - "Invalid file descriptor"
Trying other mirror.
repo id repo name status
epel/x86_64 Extra Packages for Enterprise Linux 7 - x86_64 12,631
!rhel-7-server-rpms/7Server/x86_64 Red Hat Enterprise Linux 7 Server (RPMs) 20,684
repolist: 33,315

After reading in the community about a similar problem, I tried to yum clean all. When I tried to yum repolist again, this was the output:

Loaded plugins: aliases, changelog, etckeeper, kabi, langpacks, product-id, search-disabled-repos, subscription-manager, tmprepo, verify, versionlock
Loading support for Red Hat kernel ABI
epel/x86_64/metalink | 27 kB 00:00:00
epel | 3.2 kB 00:00:00
https://cdn.redhat.com/content/dist/rhel/server/7/7Server/x86_64/os/repodata/repomd.xml: [Errno 14] curl#35 - "Invalid file descriptor"
Trying other mirror.
epel/x86_64/primary | 3.6 MB 00:00:03
epel 12631/12631
https://cdn.redhat.com/content/dist/rhel/server/7/7Server/x86_64/os/repodata/repomd.xml: [Errno 14] curl#35 - "Invalid file descriptor"
Trying other mirror.
repo id repo name status
epel/x86_64 Extra Packages for Enterprise Linux 7 - x86_64 12,631
rhel-7-server-rpms/7Server/x86_64 Red Hat Enterprise Linux 7 Server (RPMs) 0
repolist: 12,631

I tried to curl the url like mentioned in another thread, but then this error occurs:

curl -v --key /etc/pki/entitlement/6670919276622133157-key.pem --cert /etc/pki/entitlement/6670919276622133157.pem -k https://cdn.redhat.com/content/dist/rhel/server/7/7Server/x86_64/os/repodata/repomd.xml
* About to connect() to proxy proxy.winlan.net port 3125 (#0)
* Trying 172.21.10.197...
* Connected to proxy.winlan.net (172.21.10.197) port 3125 (#0)
* Establish HTTP proxy tunnel to cdn.redhat.com:443
* Proxy auth using Basic with user 'saint02'

CONNECT cdn.redhat.com:443 HTTP/1.1
Host: cdn.redhat.com:443
Proxy-Authorization: Basic c2FpbnQwMjpJbnRlcm5ldDIwMTA=
User-Agent: curl/7.29.0
Proxy-Connection: Keep-Alive

HTTP/1.1 200 Connection established

* Proxy replied OK to CONNECT request
* Initializing NSS with certpath: sql:/etc/pki/nssdb
* NSS error -12286 (SSL_ERROR_NO_CYPHER_OVERLAP)
* Cannot communicate securely with peer: no common encryption algorithm(s).
* Closing connection 0
curl: (35) Cannot communicate securely with peer: no common encryption algorithm(s).

Yum uses a proxy but it seems to work, because I needed to export the proxy before making the curl request.

Any suggestions?