What were you trying to do that didn't work?

Use post-quantum TLS 1.3 X25519MLKEM768 signature exchange with Libvirt
 

What is the impact of this issue to you?

Less secure signature exchange

Please provide the package NVR for which the bug is seen:

libvirt-11.4.0-1.el10.s390x

crypto-policies-20250602-1.gita6d4d0c.el10.noarch
openssl-3.5.0-8.el10.s390x
gnutls-3.8.9-16.el10.s390

How reproducible is this bug?:

100%

Steps to reproduce

1.  Confirm the default crypto policy is active

   server# update-crypto-policies --show
   DEFAULT

2.  (optional) Confirm ML-KEM signature and TLS 1.3 are supported

   server# cat 
    /etc/share/crypto-policies/policies/DEFAULT.pol
   ...
   group = X25519-MLKEM768 P256-MLKEM768 P384-MLKEM1024 MLKEM768-X25519
   ...
   protocol@TLS = TLS1.3 TLS1.2 DTLS1.2
   

3. Set up TLS as usual on server side and client side and confirm you can connect the client (virsh) to the server successfully, note the port that's used, e.g. 16514
4. Use openssl to establish a client connection

   openssl s_client -connect <server_ip>:16514 -CAfile /etc/pki/CA/cacert.pem </dev/null

Expected results

Negotiated TLS1.3 group: X25519MLKEM768

is in the output

Actual results

No such message is in the output, we can see the following lines that apparently confirm that the key exchange is not used

...
Peer signing digest: SHA256
Peer signature type: RSA-PSS
Server Temp Key: X25519, 253 bits
...

Additional info

Libvirt uses GnuTLS