Bugzilla – Bug 1097523
VUL-0: CVE-2018-12892: xen: libxl fails to honour readonly flag on HVM emulated SCSI disks (XSA-266)
Last modified: 2018-12-20 00:13:20 UTC
CVE-2018-12892
is public now: Xen Security Advisory CVE-2018-12892 / XSA-266 version 3 libxl fails to honour readonly flag on HVM emulated SCSI disks UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= 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. IMPACT ====== Malicious guest administrators or (in some situations) users may be able to write to supposedly read-only disk images. VULNERABLE SYSTEMS ================== 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 readonly. 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 readonly 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. MITIGATION ========== Switching to qemu-xen-traditional will avoid this vulnerability. This can be done with device_model_version="qemu-xen-traditional" in the xl configuration file. Using stub domain device models (which necessarily involves switching to qemu-xen-traditional) will also avoid this vulnerability. This can be done with device_model_stubdomain_override=true in the xl configuration file. All of these mitigations are liable to have other guest-visible effects or even regressions. It may be possible, depending on the configuration, to make the underlying storage object readonly, or to make it reject writes. CREDITS ======= This issue was discovered by Andrew Reimers of OrionVM. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa266/*.patch xen-unstable xsa266-4.10/*.patch Xen 4.10.x xsa266-4.9/*.patch Xen 4.9.x xsa266-4.8/*.patch Xen 4.8.x xsa266-4.7/*.patch Xen 4.7.x xsa266-4.6/*.patch Xen 4.6.x
SUSE-SU-2018:1981-1: An update that solves four vulnerabilities and has four fixes is now available. Category: security (important) Bug References: 1027519,1079730,1087289,1095242,1097521,1097522,1097523,1098403 CVE References: CVE-2018-12891,CVE-2018-12892,CVE-2018-12893,CVE-2018-3665 Sources used: SUSE Linux Enterprise Module for Server Applications 15 (src): xen-4.10.1_06-3.3.1 SUSE Linux Enterprise Module for Basesystem 15 (src): xen-4.10.1_06-3.3.1
SUSE-SU-2018:2059-1: An update that solves 5 vulnerabilities and has two fixes is now available. Category: security (moderate) Bug References: 1027519,1087289,1095242,1096224,1097521,1097522,1097523 CVE References: CVE-2018-11806,CVE-2018-12891,CVE-2018-12892,CVE-2018-12893,CVE-2018-3665 Sources used: SUSE Linux Enterprise Software Development Kit 12-SP3 (src): xen-4.9.2_08-3.35.2 SUSE Linux Enterprise Server 12-SP3 (src): xen-4.9.2_08-3.35.2 SUSE Linux Enterprise Desktop 12-SP3 (src): xen-4.9.2_08-3.35.2 SUSE CaaS Platform ALL (src): xen-4.9.2_08-3.35.2
openSUSE-SU-2018:2116-1: An update that solves four vulnerabilities and has four fixes is now available. Category: security (important) Bug References: 1027519,1079730,1087289,1095242,1097521,1097522,1097523,1098403 CVE References: CVE-2018-12891,CVE-2018-12892,CVE-2018-12893,CVE-2018-3665 Sources used: openSUSE Leap 15.0 (src): xen-4.10.1_06-lp150.2.6.1
openSUSE-SU-2018:2211-1: An update that solves 5 vulnerabilities and has two fixes is now available. Category: security (moderate) Bug References: 1027519,1087289,1095242,1096224,1097521,1097522,1097523 CVE References: CVE-2018-11806,CVE-2018-12891,CVE-2018-12892,CVE-2018-12893,CVE-2018-3665 Sources used: openSUSE Leap 42.3 (src): xen-4.9.2_08-25.2
released
SUSE-SU-2018:2081-2: An update that solves 5 vulnerabilities and has three fixes is now available. Category: security (important) Bug References: 1027519,1087289,1094725,1095242,1096224,1097521,1097522,1097523 CVE References: CVE-2018-11806,CVE-2018-12891,CVE-2018-12892,CVE-2018-12893,CVE-2018-3665 Sources used: SUSE Linux Enterprise Server 12-SP2-BCL (src): xen-4.7.6_02-43.36.1