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CVE-2016-9932 Xen CVE debrief

Published on 2017-01-26, CVE-2016-9932 describes a Xen x86 hypervisor flaw where CMPXCHG8B emulation mishandles a supposedly ignored operand-size prefix. In affected Xen 3.3.x through 4.7.x builds, a local HVM guest user may be able to read sensitive information from host stack memory. The NVD record rates this as low severity (CVSS 3.3) and the provided vector limits impact to confidentiality, with no direct integrity or availability effect.

Vendor
Xen
Product
CVE-2016-9932
CVSS
LOW 3.3
CISA KEV
Not listed in stored evidence
Original CVE published
2017-01-26
Original CVE updated
2026-05-13
Advisory published
2017-01-26
Advisory updated
2026-05-13

Who should care

Xen maintainers, cloud and virtualization operators running HVM guests on x86 hosts, and distro/vendor security teams that package Xen for multi-tenant environments should prioritize this advisory.

Technical summary

The issue is an information-disclosure bug in CMPXCHG8B emulation on Xen for x86 systems. According to the NVD description, a local user inside an HVM guest can influence execution through an operand-size prefix that is expected to be ignored, but instead contributes to a path that exposes host stack memory contents. NVD maps the weakness to CWE-200 and lists affected Xen versions from 3.3.0 through 4.7.0.

Defensive priority

Low overall, but worth patching in standard hypervisor maintenance because the flaw crosses the guest-to-host boundary. Prioritize faster remediation on x86 Xen deployments that host untrusted HVM guests or shared tenant workloads.

Recommended defensive actions

  • Apply the Xen vendor fix from XSA-200 and then deploy the matching package updates from your distribution or hardware vendor.
  • Confirm which x86 Xen hosts run HVM guests and inventory any systems on the affected 3.3.x through 4.7.x release range listed by NVD.
  • Use downstream advisories such as Debian DSA-3847, Gentoo GLSA 201612-56, and Citrix CTX219378 to map the fix to your exact package or appliance build.
  • Treat the issue as a confidentiality concern and verify that guest isolation assumptions do not rely on unpatched Xen versions.
  • Recheck patch status after maintenance windows, especially in hosted or multi-tenant environments where guest workloads are not fully trusted.

Evidence notes

The description and CVSS vector come from the NVD record supplied in the corpus: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N, with CWE-200 as the listed weakness. The source references include the Xen advisory XSA-200 and downstream advisories from Debian, Gentoo, and Citrix. The provided timeline shows publication on 2017-01-26 and a later NVD modification on 2026-05-13; no KEV entry is supplied in the corpus.

Official resources

Publicly disclosed in the supplied NVD record on 2017-01-26 and later modified on 2026-05-13. No CISA KEV entry is included in the provided corpus.