| Reported on: | 20171005 |
|---|---|
| Published on: | 20171016 |
| Fixed on: | 20171016 |
| Reported by: | Daniel P. Berrange |
|---|---|
| Patched by: | Daniel P. Berrange |
The default_tls_x509_verify (and related) parameters in qemu.conf control whether the TLS servers in QEMU request & verify certificates from clients. This works as a simple access control system for QEMU servers by requiring the CA to issue certs to permitted clients. This use of client certificates is disabled by default, since it requires extra work to issue client certificates. Unfortunately the libvirt code was using these configuration parameters when setting up both TLS clients and servers in QEMU. The result was that TLS clients for character devices and disk devices had verification turned off, meaning they would ignore any errors while validating the server certificate.
A MITM attacker can attack any client connection made by QEMU's character devices and disk devices which have TLS enabled. The attacker can send an arbitrary certificate back to the client QEMU and it will ignore all errors that result during validation.
Enable the 'default_tls_x509_verify' parameter in qemu.conf restart libvirtd. This will trigger libvirt to turn on certificate verification in QEMU clients. Unfortunately this will also turn on use of client certificates in QEMU servers.