Libvirt Security Notice: LSN-2014-0003

Unsafe parsing of XML documents allows arbitrary file read

Lifecycle

Credits

See also

• CVE-2014-0179

Description

When parsing XML documents, libvirt passes the XML_PARSE_NOENT flag to libxml2 which instructs it to expand all entities in the XML document during parsing. This can be used to insert the contents of host OS files in the resulting parsed content. Although the flaw was introduced in 0.0.5, it was dormant having no ill effects, since the APIs involved all required the user to authenticate with privileges equivalent to root. In version 0.7.5 or later the virConnectCompareCPU / virConnectBaselineCPU methods activate the dormant bug, allowing for denial of service. In version 1.0.0 or later, if the admin opts in to using the new fine grained access control feature, there is potential for unprivileged information disclosure.

Impact

A malicious user can pass libvirt an XML document which contains an entity that points to an arbitrary file on the host. When libvirt parses this document, it will insert the contents of that host file, which could allow the user to read the contents of files that they otherwise do not have permission to view. It also has the potential to cause a denial of service / indefinite hang of libvirt, if the entity points to a named pipe with no writer connected or certain proc files. If the libvirt installation is not using fine grained access control then virConnectCompareCPU and virConnectBaselineCPU APIs can be used by a read-only user to inflict a denial of service attack. If the libvirt installation is using fine grained access control, then as well as the denial of service attack, one or more of the following APIs can be used for information disclosure of files: virDomainDefineXML, virNetworkCreateXML, virNetworkDefineXML, virStoragePoolCreateXML, virStoragePoolDefineXML, virStorageVolCreateXML, virDomainCreateXML, virNodeDeviceCreateXML, virInterfaceDefineXML, virStorageVolCreateXMLFrom, virConnectDomainXMLFromNative, virConnectDomainXMLToNative, virSecretDefineXML, virNWFilterDefineXML, virDomainSnapshotCreateXML, virDomainSaveImageDefineXML, virDomainCreateXMLWithFiles, virConnectCompareCPU, virConnectBaselineCPU.

Workaround

Stop use of the fine grained access control mechanism, and restrict access to all the libvirt TCP/UNIX sockets to only trusted authenticated users. Simply denying access to the affected APIs in the access control policy is insufficient to mitigate the bug, since the XML document typically needs to be parsed before the access control check is applied in order to extra the UUID/name of the object to check. Access to the readonly libvirt socket must also be revoked

Affected product: libvirt

Alternative formats: [xml] [text]