CVE-2018-12892 Information

Description

An issue was discovered in Xen 4.7 through 4.10.x. libxl fails to pass the readonly flag to qemu when setting up a SCSI disk due to what was probably an erroneous merge conflict resolution. Malicious guest administrators or (in some situations) users may be able to write to supposedly read-only disk images. Only emulated SCSI disks (specified as \sd\ in the libxl disk configuration or an equivalent) are affected. IDE disks (\hd) are not affected (because attempts to make them readonly are rejected). Additionally CDROM devices (that is devices specified to be presented to the guest as CDROMs regardless of the nature of the backing storage on the host) are not affected; they are always read only. Only systems using qemu-xen (rather than qemu-xen-traditional) as the device model version are vulnerable. Only systems using libxl or libxl-based toolstacks are vulnerable. (This includes xl and libvirt with the libxl driver.) The vulnerability is present in Xen versions 4.7 and later. (In earlier versions provided that the patch for XSA-142 has been applied attempts to create read only disks are rejected.) If the host and guest together usually support PVHVM the issue is exploitable only if the malicious guest administrator has control of the guest kernel or guest kernel command line.

CVSS Vector

CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Reference

http://www.openwall.com/lists/oss-security/2018/06/27/12 http://www.securityfocus.com/bid/104571 http://www.securitytracker.com/id/1041203 http://xenbits.xen.org/xsa/advisory-266.html https://security.gentoo.org/glsa/201810-06 https://www.debian.org/security/2018/dsa-4236

Attack Complexity

LOW

Privileges Required

LOW

User Interaction Required

LOW

Scope

NONE

Confidentiality Impact

CHANGED

Integrity Impact

HIGH

Availability Impact

HIGH

Base Score

HIGH

Base Severity

9.9