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CVE-2018-12892

Published: 2 July 2018

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.

Notes

AuthorNote
mdeslaur
hypervisor packages are in universe. For
issues in the hypervisor, add appropriate
tags to each section, ex:
Tags_xen: universe-binary

Priority

Medium

Cvss 3 Severity Score

9.9

Score breakdown

Status

Package Release Status
xen
Launchpad, Ubuntu, Debian
artful Ignored
(end of life)
bionic Needed

cosmic Ignored
(end of life)
disco Ignored
(end of life)
eoan Ignored
(end of life)
focal Not vulnerable
(4.8.3+xsa267+shim4.10.1+xsa267-1+deb9u9)
groovy Ignored
(end of life)
hirsute Ignored
(end of life)
impish Ignored
(end of life)
jammy Not vulnerable
(4.8.3+xsa267+shim4.10.1+xsa267-1+deb9u9)
kinetic Not vulnerable
(4.8.3+xsa267+shim4.10.1+xsa267-1+deb9u9)
lunar Not vulnerable
(4.8.3+xsa267+shim4.10.1+xsa267-1+deb9u9)
mantic Not vulnerable
(4.8.3+xsa267+shim4.10.1+xsa267-1+deb9u9)
noble Not vulnerable
(4.8.3+xsa267+shim4.10.1+xsa267-1+deb9u9)
trusty Does not exist
(trusty was needs-triage)
upstream
Released (4.8.3+xsa267+shim4.10.1+xsa267-1+deb9u9)
xenial Not vulnerable
(code not present)
Binaries built from this source package are in Universe and so are supported by the community.

Severity score breakdown

Parameter Value
Base score 9.9
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction None
Scope Changed
Confidentiality High
Integrity impact High
Availability impact High
Vector CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H