# CVE-2016-9383: Xen broken bit test instruction emulation memory corruption

Source: https://junglewise.ai/threats/cve-2016-9383-xen-broken-bit-test-instruction-emulation-memory-corruption  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2017-01-23. Updated: 2026-05-13  
License: CC BY 4.0 with a link back

CVE-2016-9383 · Severity: high · CVSS 8.8 · Published 2017-01-23

Xen is a virtualization platform that allows multiple operating systems to run on a single physical server. A flaw in how it handles certain processor instructions allows a user inside a virtual machine to break out and access the underlying host system. This could result in the attacker stealing data from other virtual machines, crashing the entire server, or taking full control of the host hardware.

Technologies: [Citrix Xenserver](https://junglewise.ai/threats/technologies/xenserver), [Xen Project Xen](https://junglewise.ai/threats/technologies/xen). Vendors: [Citrix](https://junglewise.ai/threats/vendors/citrix), [Xen Project](https://junglewise.ai/threats/vendors/xen-project).

## Quick answers

**Is CVE-2016-9383 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2016-9383 being exploited in the wild.

**How severe is CVE-2016-9383?** High severity, with a CVSS score of 8.8, published 23 January 2017.

**Which products and versions are affected?** Citrix Xenserver 6.0.2, 6.2.0, 6.5, 7.0; Xen Project Xen All versions (exposed to 64-bit x86 guests).

**Is there a fix for CVE-2016-9383?** A patch was published on 2016-11-22: Patch released by Xen Project Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2016-9383 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2016-9383?** Check whether you run Citrix Xenserver or Xen Project Xen at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability exists in Xen's emulation of x86 bit test instructions (BT, BTC, BTR, and BTS) when used with a destination memory operand and a source register. During emulation, Xen incorrectly recalculates the memory address and register operand, discarding high bits of an intermediate expression. This logic error allows a malicious 64-bit guest to cause the hypervisor to perform unintended memory accesses or register updates. An attacker can leverage this to achieve arbitrary memory modification on the host, leading to host crashes (DoS), information disclosure, or full host-level privilege escalation. The issue is primarily exposed to 64-bit x86 guests; on Xen 4.7 and later, it typically requires specific guest privileges or non-default CPU configurations to exploit.

## Affected products

- Xen Project Xen All versions (exposed to 64-bit x86 guests)
- Citrix XenServer 6.0.2, 6.2.0, 6.5, 7.0

## Timeline

- 2016-11-22: disclosed: Initial public release of XSA-195
- 2016-11-22: patched: Patch released by Xen Project
- 2017-01-23: advisory: NVD publication date

## References

- [http://www.securityfocus.com/bid/94474](http://www.securityfocus.com/bid/94474)
- [http://www.securitytracker.com/id/1037346](http://www.securitytracker.com/id/1037346)
- [http://xenbits.xen.org/xsa/advisory-195.html](http://xenbits.xen.org/xsa/advisory-195.html)
- [https://security.gentoo.org/glsa/201612-56](https://security.gentoo.org/glsa/201612-56)
- [https://support.citrix.com/article/CTX218775](https://support.citrix.com/article/CTX218775)

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