Libvirt Security Notice: LSN-2015-0004

ACL bypass using ../ to access beyond storage pool

Lifecycle

Credits

See also

• CVE-2015-5313
• FICORA bug #876194

Description

Various virStorageVol* API operate on user-supplied volume names by concatenating the volume name to the pool location. Note that the virStoragePoolListVolumes API, when used on a storage pool backed by a directory in a file system, will only list volumes immediately in that directory (there is no traversal into subdirectories). However, other APIs such as virStorageVolCreateXML were not checking if a potential volume name represented one of the volumes that could be returned by virStoragePoolListVolumes; because they were not rejecting the use of '/' in a volume name.

Impact

Because no checking was done on volume names, a user could supply a potential volume name of something like '../../../etc/passwd' to attempt to access a file not belonging to the storage pool. When fine-grained Access Control Lists (ACL) are in effect, a user with storage_vol:create ACL permission but lacking domain:write permssion could thus abuse virStorageVolCreateXML and similar APIs to gain access to files not normally permitted to that user. Fortunately, it appears that the only APIs that could leak information or corrupt files require read-write connection to libvirtd; and when ACLs are not in use (the default without any further configuration), a user with read-write access can already be considered to have full access to the machine, and without an escalation of privilege there is no security problem.

Workaround

If fine-grained ACLs must be used, administrators must consider all of the storage_vol:* permissions as equivalent to domain:write when running an impacted version of libvirt. The easiest way to prevent untrusted users from gaining unauthorized access to volumes outside of permitted pools is by disabling the use of fine-graned ACLs, and ensuring that such users do not have read-write access to libvirtd.

Affected product: libvirt

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