Vulnerability identifier: #VU31979

Vulnerability risk: Medium

CVSSv3.1: 5.9 [CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:U/RL:O/RC:C]

CVE-ID: CVE-2019-19583

CWE-ID: CWE-399

Exploitation vector: Local network

Exploit availability: No

Vulnerable software:
Xen
Server applications / Virtualization software

Vendor: Xen Project

Description

The vulnerability allows a remote user to perform a denial of service (DoS) attack.

An issue was discovered in Xen through 4.12.x allowing x86 HVM/PVH guest OS users to cause a denial of service (guest OS crash) because VMX VMEntry checks mishandle a certain case. Please see XSA-260 for background on the MovSS shadow. Please see XSA-156 for background on the need for #DB interception. The VMX VMEntry checks do not like the exact combination of state which occurs when #DB in intercepted, Single Stepping is active, and blocked by STI/MovSS is active, despite this being a legitimate state to be in. The resulting VMEntry failure is fatal to the guest. HVM/PVH guest userspace code may be able to crash the guest, resulting in a guest Denial of Service. All versions of Xen are affected. Only systems supporting VMX hardware virtual extensions (Intel, Cyrix, or Zhaoxin CPUs) are affected. Arm and AMD systems are unaffected. Only HVM/PVH guests are affected. PV guests cannot leverage the vulnerability.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

Xen: 4.8.0 - 4.12.1

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External links
http://lists.opensuse.org/opensuse-security-announce/2020-01/msg00011.html
http://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/34HBFTYNMQMWIO2GGK7DB6KV4M6R5YPV/
http://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/D5R73AYE53QA32KTMHUVKCX6E52CIS43/
http://seclists.org/bugtraq/2020/Jan/21
http://security.gentoo.org/glsa/202003-56
http://www.debian.org/security/2020/dsa-4602
http://xenbits.xen.org/xsa/advisory-308.html

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote authenticated user via the local network (LAN).

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.