ID CVE-2019-18425
Summary An issue was discovered in Xen through 4.12.x allowing 32-bit PV guest OS users to gain guest OS privileges by installing and using descriptors. There is missing descriptor table limit checking in x86 PV emulation. When emulating certain PV guest operations, descriptor table accesses are performed by the emulating code. Such accesses should respect the guest specified limits, unless otherwise guaranteed to fail in such a case. Without this, emulation of 32-bit guest user mode calls through call gates would allow guest user mode to install and then use descriptors of their choice, as long as the guest kernel did not itself install an LDT. (Most OSes don't install any LDT by default). 32-bit PV guest user mode can elevate its privileges to that of the guest kernel. Xen versions from at least 3.2 onwards are affected. Only 32-bit PV guest user mode can leverage this vulnerability. HVM, PVH, as well as 64-bit PV guests cannot leverage this vulnerability. Arm systems are unaffected.
Vulnerable Configurations
  • cpe:2.3:o:xen:xen:4.8.0:*:*:*:*:*:x86:*
Base: 9.3 (as of 14-11-2019 - 16:15)
  • Privilege Escalation
    An adversary exploits a weakness enabling them to elevate their privilege and perform an action that they are not supposed to be authorized to perform.
  • Privilege Abuse
    An adversary is able to exploit features of the target that should be reserved for privileged users or administrators but are exposed to use by lower or non-privileged accounts. Access to sensitive information and functionality must be controlled to ensure that only authorized users are able to access these resources. If access control mechanisms are absent or misconfigured, a user may be able to access resources that are intended only for higher level users. An adversary may be able to exploit this to utilize a less trusted account to gain information and perform activities reserved for more trusted accounts. This attack differs from privilege escalation and other privilege stealing attacks in that the adversary never actually escalates their privileges but instead is able to use a lesser degree of privilege to access resources that should be (but are not) reserved for higher privilege accounts. Likewise, the adversary does not exploit trust or subvert systems - all control functionality is working as configured but the configuration does not adequately protect sensitive resources at an appropriate level.
  • Restful Privilege Elevation
    Rest uses standard HTTP (Get, Put, Delete) style permissions methods, but these are not necessarily correlated generally with back end programs. Strict interpretation of HTTP get methods means that these HTTP Get services should not be used to delete information on the server, but there is no access control mechanism to back up this logic. This means that unless the services are properly ACL'd and the application's service implementation are following these guidelines then an HTTP request can easily execute a delete or update on the server side. The attacker identifies a HTTP Get URL such as http://victimsite/updateOrder, which calls out to a program to update orders on a database or other resource. The URL is not idempotent so the request can be submitted multiple times by the attacker, additionally, the attacker may be able to exploit the URL published as a Get method that actually performs updates (instead of merely retrieving data). This may result in malicious or inadvertent altering of data on the server.
cvss-vector via4 AV:N/AC:M/Au:N/C:C/I:C/A:C
refmap via4
bugtraq 20200114 [SECURITY] [DSA 4602-1] xen security update
debian DSA-4602
  • FEDORA-2019-376ec5c107
  • FEDORA-2019-865bb16900
  • FEDORA-2019-cbb732f760
gentoo GLSA-202003-56
mlist [oss-security] 20191031 Xen Security Advisory 298 v3 (CVE-2019-18425) - missing descriptor table limit checking in x86 PV emulation
suse openSUSE-SU-2019:2506
Last major update 14-11-2019 - 16:15
Published 31-10-2019 - 14:15
Last modified 14-11-2019 - 16:15
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