Libvirt Security Notice: LSN-2017-0002 ====================================== Summary: TLS certificate verification disabled for clients Reported on: 20171005 Published on: 20171016 Fixed on: 20171016 Reported by: Daniel P. Berrange <berrange(a)redhat.com&gt; Patched by: Daniel P. Berrange <berrange(a)redhat.com&gt; See also: CVE-2017-1000256 Description ----------- 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. Impact ------ 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. Workaround ---------- 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. Affected product ---------------- Name: libvirt Repository: git://libvirt.org/git/libvirt.git http://libvirt.org/git/?p=libvirt.git Branch: master Broken in: v2.3.0 Broken in: v2.4.0 Broken in: v2.5.0 Broken in: v3.0.0 Broken in: v3.1.0 Broken in: v3.2.0 Broken in: v3.3.0 Broken in: v3.4.0 Broken in: v3.5.0 Broken in: v3.6.0 Broken in: v3.7.0 Broken in: v3.8.0 Fixed in: v3.9.0 Broken by: ce61c16450d4992612d1fc6f39a39e79bfccead5 Fixed by: 441d3eb6d1be940a67ce45a286602a967601b157 Branch: v3.0-maint Broken by: ce61c16450d4992612d1fc6f39a39e79bfccead5 Fixed by: 16daadc708be65c2681f54d33ac4004ccaf6e82d Branch: v3.2-maint Broken in: v3.2.1 Broken by: ce61c16450d4992612d1fc6f39a39e79bfccead5 Fixed by: 9e6bc47bb541d8eea10cdd5704ea7f5e699bf0ba Branch: v3.7-maint Broken by: ce61c16450d4992612d1fc6f39a39e79bfccead5 Fixed by: dc6c41798d1eb5c52c75365ffa22f7672709dfa7 Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|