XenserverApplication · Citrix
CVE-2016-9381
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedRace condition in QEMU in Xen allows local x86 HVM guest OS administrators to gain privileges by changing certain data on shared rings, aka a "double fetch" vulnerability.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceA race condition (double-fetch vulnerability) in QEMU within Xen allows x86 HVM guest administrators to escalate privileges by manipulating data on shared rings between the guest and hypervisor. The attacker exploits the window between initial data fetch and subsequent use to modify the data, bypassing validation.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
XenserverApplication
= 6.0.2= 6.2.0= 6.5= 7.0<= 2.7.1= 2.8.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- High
- Privileges
- High
- User interaction
- None
- Scope
- Changed
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify Xen hypervisor versionRun `xl info` or check /etc/xensource-inventory on the Xen host to obtain the Xen versionAffected if Version matches Citrix Xenserver 6.0.2, 6.2.0, 6.5, or 7.0
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Check QEMU version used by XenQuery the QEMU version via `xl dm-info <domain_id>` or check the installed qemu package with `rpm -q qemu` or `dpkg -l qemu`Affected if QEMU version is 2.8.0 or earlier than or equal to 2.7.1
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Verify x86 HVM guests are presentList all VMs with `xl list` and check the type column; look for 'HVM' type domainsAffected if Any x86-based HVM (Hardware Virtual Machine) guests are configured or running
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Confirm shared ring interface is in useInspect VM configuration files in /etc/xen/<vm_name> or via `xl cfgread <vm_name>` for 'hap' or 'shared_ring' settings; check if the guest uses emulated devices with shared memory ringsAffected if HVM guests are using the default QEMU device model with paravirtualized drivers or emulated devices that rely on shared ring buffers between guest and hypervisor
You are affected if your Citrix Xenserver version is 6.0.2, 6.2.0, 6.5, or 7.0, or your QEMU version is 2.8.0 or <= 2.7.1, AND you are running x86 HVM guests that utilize the shared ring interface with the QEMU device model.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataApply Xen security patches addressing the double-fetch vulnerability in QEMU's shared ring handling for x86 HVM guests. Upgrade to patched Xen versions that include the fix.
Fix this in Xenserver
Scoped from the published advisory
- Consultation4.0 h
- Implementation10.0 h
- Testing8.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,944.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2016-9381 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2016-9381 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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