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XenserverApplication · Citrix

CVE-2016-1571

MEDIUM · 6.3 CVSS v3.0 Published 2016-01-22
Fix available
A fix is available. Upgrade to after 6.5 or later.
See remediation →
69/100
Remediation priority · Elevated
Remotely reachable Zero-click

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 · unedited
The paging_invlpg function in include/asm-x86/paging.h in Xen 3.3.x through 4.6.x, when using shadow mode paging or nested virtualization is enabled, allows local HVM guest users to cause a denial of service (host crash) via a non-canonical guest address in an INVVPID instruction, which triggers a hypervisor bug check.

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 confidence

The vulnerability exists in Xen's paging_invlpg function when shadow mode paging or nested virtualization is enabled. A local HVM guest can trigger a hypervisor bug check by providing a non-canonical address in an INVVPID instruction, causing the host to crash.

MitigationApply the appropriate Xen security patch for CVE-2016-1571. If immediate patching is not possible, consider disabling shadow mode paging or nested virtualization in affected guest configurations as a temporary workaround.

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
Affected:<= 6.5
XenOperating system
Affected:= 3.3.0= 3.3.1= 3.3.2= 3.4.0= 3.4.1= 3.4.2= 3.4.3= 3.4.4= 4.1.0= 4.1.1= 4.1.2= 4.1.3

CVSS 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
Network
Complexity
High
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify Xen hypervisor version
    Run 'xm version' or 'xl version' to display the Xen hypervisor version. On Citrix Xenserver, check the XS Build number via 'xe host-list' and 'xe host-param-get param-name=product_version'.
    Affected if The version matches one listed in affected ranges: Citrix Xenserver <= 6.5, or Xen versions 3.3.0, 3.3.1, 3.3.2, 3.4.0, 3.4.1, 3.4.2, 3.4.3, 3.4.4, 4.1.0, 4.1.1, 4.1.2, or 4.1.3.
  2. Confirm running HVM guests
    List all guests using 'xl list' or 'xe vm-list' and verify any have type 'HVM' in their configuration. Check guest configuration with 'xl cfglist <vmname>' or 'xe vm-param-list uuid=<uuid>' for HVM domains.
    Affected if Any HVM (Hardware Virtual Machine) guests are running on the affected Xen host.
  3. Check if shadow mode paging is enabled
    Review guest configuration files for 'shadow_memory' setting or use 'xl list -l <vmname>' to inspect the shadow mode configuration. On Xen, shadow mode is enabled by setting 'shadow_memory' in the guest config or via 'xl set-parameters shadow-mode=y'. For Citrix, check via 'xe vm-param-list' for the HVM VM.
    Affected if Shadow mode paging is explicitly enabled in any guest configuration or globally on the host.
  4. Check if nested virtualization is enabled
    Inspect guest configuration for 'nestedhvm' or 'hap' settings using 'xl cfglist <vmname>' or 'xe vm-param-list'. Also check 'xl dmesg' for nested virtualization status. Look for 'nestedhvm=1' in guest config files.
    Affected if Nested virtualization (nestedhvm) is enabled for any guest, allowing a guest to run its own hypervisor.

A system is affected if it runs a vulnerable Xen version (as listed above) AND has either shadow mode paging or nested virtualization enabled for any HVM guest, allowing that guest to trigger the bug via a non-canonical address in an INVVPID instruction.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Upgrade available Upgrade to a release after 6.5
Interim mitigation

Apply the appropriate Xen security patch for CVE-2016-1571. If immediate patching is not possible, consider disabling shadow mode paging or nested virtualization in affected guest configurations as a temporary workaround.

Fix this in Xenserver Scoped from the published advisory
  • Consultation4.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,880
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2016-1571 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data