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Vm ServerOperating system · Oracle

CVE-2016-4962

MEDIUM · 6.7 CVSS v3.0 Published 2016-06-07
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
69/100
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
The libxl device-handling in Xen 4.6.x and earlier allows local OS guest administrators to cause a denial of service (resource consumption or management facility confusion) or gain host OS privileges by manipulating information in guest controlled areas of xenstore.

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 libxl device-handling code in Xen 4.6.x and earlier fails to properly validate or sanitize information in guest-controlled areas of xenstore, allowing a malicious local guest administrator to manipulate these values. This manipulation can cause denial of service through resource exhaustion or management facility confusion, or potentially enable privilege escalation to gain host OS privileges.

MitigationUpgrade to Xen 4.6.1 or later, or apply the relevant security patches. If upgrading is not immediately feasible, restrict local guest administrator access and monitor xenstore activity for anomalous modifications.

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
Vm ServerOperating system
Affected:= 3.3= 3.4
XenOperating system
Affected:= 4.3.0= 4.3.1= 4.3.2= 4.3.3= 4.3.4= 4.4.0= 4.4.1= 4.4.2= 4.4.3= 4.4.4= 4.5.0= 4.5.1

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
Low
Privileges
High
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

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

  1. Identify installed Xen version
    Run 'xl version' or 'xm version' on the host to obtain the Xen hypervisor version number. Alternatively, check the package manager: 'rpm -q xen' or 'dpkg -l | grep xen' depending on distribution.
    Affected if The installed version matches 4.3.0 through 4.6.x (specifically 4.3.0-4.3.4, 4.4.0-4.4.4, 4.5.0-4.5.1, or any 4.6.x version before 4.6.1).
  2. Confirm libxl is the active device model
    Check which device model is in use for VMs. Examine the VM configuration file or run 'xl list -l <vmname>' and look for the 'device_model' field. If it is set to 'libxl' or uses the default libxl-based qemu, the system uses the affected libxl code path.
    Affected if The device model uses libxl (the default in Xen 4.4+). This is the case for most modern Xen setups using xl toolstack.
  3. Verify xenstore daemon is running
    Run 'ps aux | grep xenstore' to confirm xenstored or xenstore-daemon is active. Also check if '/var/run/xenstored' socket exists.
    Affected if xenstore is active and accessible to guest VMs, which is the default configuration for paravirtualized guests.
  4. Review xenstore access controls
    Examine the xenstore configuration files (typically in /etc/xen or via xl configuration) for any restrictions on guest write access to device tree paths. Use 'xenstore-ls' to view current xenstore contents and check for unexpected or unusually large entries in guest-controlled paths.
    Affected if Guests have write access to arbitrary xenstore paths without validation, allowing manipulation of device-handling values.
  5. Audit guest VM configurations for local admin access
    Review the VM configuration files to identify which guests have local administrator or root access. Check for any VMs configured with untrusted local guest administrators who could exploit this flaw.
    Affected if There are untrusted local guest administrators with root privileges in any VM running on the affected Xen host.

A host is affected if it runs Xen 4.6.x or earlier (specifically versions 4.3.0-4.5.1 or 4.6.0) with libxl as the device model, has xenstore accessible to guests, and contains untrusted local guest administrators who could manipulate xenstore values.

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

Upgrade to Xen 4.6.1 or later, or apply the relevant security patches. If upgrading is not immediately feasible, restrict local guest administrator access and monitor xenstore activity for anomalous modifications.

Fix this in Vm Server Scoped from the published advisory
  • Consultation6.0 h
  • Implementation12.0 h
  • Testing10.0 h
  • Review / QA6.0 h
34.0 hours of engineering $5,940
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Scan for this in your stack

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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-2016-4962 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