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XenOperating system

CVE-2017-12855

MEDIUM · 6.5 CVSS v3.0 Published 2017-08-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
67/100
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
Xen maintains the _GTF_{read,writ}ing bits as appropriate, to inform the guest that a grant is in use. A guest is expected not to modify the grant details while it is in use, whereas the guest is free to modify/reuse the grant entry when it is not in use. Under some circumstances, Xen will clear the status bits too early, incorrectly informing the guest that the grant is no longer in use. A guest may prematurely believe that a granted frame is safely private again, and reuse it in a way which contains sensitive information, while the domain on the far end of the grant is still using the grant. Xen 4.9, 4.8, 4.7, 4.6, and 4.5 are affected.

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 is a grant table race condition in Xen's para-virtualization mechanism where GTF_reading/writing status bits are cleared prematurely, incorrectly indicating to a guest OS that a granted memory frame is no longer in use. A malicious guest can therefore reuse the grant entry while the remote domain still holds an active reference, potentially exposing sensitive data from another guest's memory.

MitigationApply the relevant Xen security patch for CVE-2017-12855 to affected versions (4.5-4.9) or upgrade to a patched Xen release. Guests should not be granted uncontrolled access to grant tables without monitoring.

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
XenOperating system
Affected:= 4.5.0= 4.5.1= 4.5.2= 4.5.3= 4.5.5= 4.6.0= 4.6.1= 4.6.3= 4.6.4= 4.6.5= 4.6.6= 4.7.0

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
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.0/AV:L/AC:L/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 installed Xen version
    Run 'xl info' or 'xm info' and look for the 'xen_version' field, or check the package version with 'rpm -q xen' (RHEL/CentOS) or 'dpkg -l xen*' (Debian/Ubuntu)
    Affected if The version matches any of: 4.5.0, 4.5.1, 4.5.2, 4.5.3, 4.5.5, 4.6.0, 4.6.1, 4.6.3, 4.6.4, 4.6.5, 4.6.6, 4.7.0
  2. List running guest domains
    Run 'xl list' or 'xm list' to see all domains currently running on the Xen host
    Affected if Any paravirtualized (PV) guests are listed as running (HVM guests are not affected by this specific flaw)
  3. Verify grant table usage
    Run 'xl list -l <domain>' for each running guest to inspect the domain configuration, looking for 'grant_tables' or 'pt_mode' settings in the disk or network configuration
    Affected if Any guest has grant table access configured (the vulnerability only applies when grant tables are in use)
  4. Check for untrusted guest workloads
    Review which guests have access to grant table interfaces by examining the domain configuration files in /etc/xen/ or via 'xl dmidecode' for guest classification
    Affected if Any guest that is not fully trusted has been granted direct access to grant table operations

You are affected if your Xen host runs version 4.5.0 through 4.7.0 and hosts paravirtualized guests that have grant table access enabled.

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 the relevant Xen security patch for CVE-2017-12855 to affected versions (4.5-4.9) or upgrade to a patched Xen release. Guests should not be granted uncontrolled access to grant tables without monitoring.

Fix this in Xen Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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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-2017-12855 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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