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XenserverApplication · Citrix

CVE-2018-3665

MEDIUM · 5.6 CVSS v3.1 Published 2018-06-21
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
58/100
Remediation priority · Elevated
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
System software utilizing Lazy FP state restore technique on systems using Intel Core-based microprocessors may potentially allow a local process to infer data from another process through a speculative execution side channel.

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 · moderate confidence

This vulnerability exploits the Lazy FP state restore mechanism in Intel Core processors. When context switching occurs, instead of immediately saving/restoring FPU state (for performance), the system lazily restores it only when a process actually uses floating-point instructions. Through speculative execution side channels, a malicious local process can potentially infer floating-point register values from another process that was previously scheduled on the same CPU core.

MitigationApply CPU microcode/firmware updates from Intel and OS-level security patches. Alternatively, disable Lazy FP state restore in the kernel (Linux: 'eagerfpu=on' kernel parameter) to force immediate FPU state saving, though this may incur a performance penalty.

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:= 7.0= 7.1= 7.3= 7.4= 7.5
Ubuntu LinuxOperating system
Affected:= 12.04= 14.04= 16.04
Debian LinuxOperating system
Affected:= 8.0= 9.0
FreeBSDOperating system
Affected:= 11.0= 11.1= 11.2
Enterprise LinuxOperating system
Affected:= 6.0= 7.0
Enterprise Linux DesktopOperating system
Affected:= 6.0= 7.0
Enterprise Linux WorkstationOperating system
Affected:= 6.0= 7.0
Core I3Hardware / appliance
Affected:= 330e= 330m= 330um= 350m= 370m= 380m= 380um= 390m= 530= 540= 550= 560

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

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N

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 CPU processor
    Run 'cat /proc/cpuinfo' or 'lscpu' and look for Intel Core processor model numbers in the list: 330e, 330m, 330um, 350m, 370m, 380m, 380um, 390m, 530, 540, 550, 560
    Affected if CPU model matches one of these Intel Core identifiers AND the system uses Lazy FP state restore (see step 3)
  2. Check operating system version
    Run 'uname -a' or check /etc/os-release (Linux), or system version commands for other affected OSes
    Affected if OS is Ubuntu 12.04, 14.04, or 16.04; Debian 8.0 or 9.0; FreeBSD 11.0, 11.1, or 11.2; RHEL 6.0 or 7.0; or Citrix Xenserver 7.0, 7.1, 7.3, 7.4, or 7.5
  3. Check kernel FPU state restore configuration
    On Linux, examine kernel command line in /proc/cmdline for 'eagerfpu=on' (which disables lazy restore) or 'eagerfpu=off' (vulnerable). Also check /sys/kernel/debug/x86/fpu_info if available.
    Affected if Kernel does not have 'eagerfpu=on' parameter set, indicating Lazy FP state restore is active (vulnerable configuration)
  4. Verify hypervisor context
    If running as a virtual machine, check hypervisor with 'systemd-detect-virt' or 'virt-what'. For Citrix Xenserver, check version with 'xl version' or xe host-list
    Affected if System is running on Citrix Xenserver 7.0, 7.1, 7.3, 7.4, or 7.5 hypervisor without microcode updates applied

A system is affected if it runs on a vulnerable Intel Core processor listed above, uses an affected OS version, and has Lazy FP state restore enabled (eagerfpu not set to 'on' in kernel).

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply CPU microcode/firmware updates from Intel and OS-level security patches. Alternatively, disable Lazy FP state restore in the kernel (Linux: 'eagerfpu=on' kernel parameter) to force immediate FPU state saving, though this may incur a performance penalty.

Fix this in Xenserver Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
20.0 hours of engineering $3,500
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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-2018-3665 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