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CVE-2018-12892: Xen: Exposure of Sensitive Information to an Unauthorized Actor

CVE-2018-12892 is rated critical with a CVSS v3.0 base score of 9.9 and affects Xen, along with 1 other product in NVD’s configuration data. Per its scoring, it can be exploited over the network, without any user interaction. The scored impact on confidentiality, integrity and availability is the highest available.

Vulnerability 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.

Severity breakdown

CVSS v3.0 9.9: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

  • Attack vector: Network. Exploitable remotely over the network, with no need for local or physical access.
  • Attack complexity: Low. No special conditions; the attack can be repeated reliably.
  • Privileges required: Low. A basic user account is enough.
  • User interaction: None. No action from any user is needed.
  • Scope: Changed. Impact reaches beyond the vulnerable component to other resources.
  • Confidentiality impact: High. Total loss of confidentiality; sensitive data can be fully disclosed.
  • Integrity impact: High. Total loss of integrity; data or system state can be fully modified.
  • Availability impact: High. Total loss of availability; the component can be shut down.

Underlying weakness

CWE-200: Exposure of Sensitive Information to an Unauthorized Actor

The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.

Affected products

  • Xen: from 4.7.0 up to and including 4.10.1
  • Debian Linux: 9.0

References