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XenserverApplication · Citrix

CVE-2016-9603

CRITICAL · 9.9 CVSS v3.0 Published 2018-07-27
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
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
A heap buffer overflow flaw was found in QEMU's Cirrus CLGD 54xx VGA emulator's VNC display driver support before 2.9; the issue could occur when a VNC client attempted to update its display after a VGA operation is performed by a guest. A privileged user/process inside a guest could use this flaw to crash the QEMU process or, potentially, execute arbitrary code on the host with privileges of the QEMU process.

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

Heap buffer overflow in QEMU's Cirrus CLGD 54xx VGA emulator's VNC display driver (before v2.9). Triggered when a VNC client updates its display after a guest performs a VGA operation, allowing a privileged guest user to potentially execute arbitrary code on the host with QEMU process privileges.

MitigationUpgrade QEMU to version 2.9 or later to patch this vulnerability. If immediate upgrading is not feasible, restrict VNC access to trusted guests and consider network segmentation.

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:= 6.0.2= 6.2.0= 6.5= 7.0= 7.1
OpenstackApplication
Affected:= 5.0= 6.0= 7.0= 8= 9= 10
Debian LinuxOperating system
Affected:= 7.0
Enterprise Linux DesktopOperating system
Affected:= 6.0= 7.0
Enterprise Linux ServerOperating system
Affected:= 6.0= 7.0
Enterprise Linux Server AusOperating system
Affected:= 7.3= 7.4
Enterprise Linux Server EusOperating system
Affected:= 7.3= 7.4= 7.5
Enterprise Linux WorkstationOperating system
Affected:= 6.0= 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
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.0/AV:N/AC:L/PR:L/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 checks

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

  1. Identify QEMU version
    Run 'qemu-system-x86_64 --version' or check the package version via 'rpm -q qemu-kvm' (RHEL) or 'dpkg -l qemu*' (Debian)
    Affected if The installed QEMU version is earlier than 2.9 and the package contains the VNC display driver component
  2. Check if Cirrus VGA emulator is configured
    Examine the QEMU command line or libvirt domain XML for '-vga cirrus' or look for the cirrus video device in the domain configuration
    Affected if The virtual machine is configured to use the Cirrus CLGD 54xx VGA emulator (vga model set to cirrus)
  3. Verify VNC display is enabled
    Look for '-vnc' option in the QEMU command line, or check libvirt domain XML for '<graphics type="vnc">' configuration, or inspect netstat/tcpdump for listening VNC ports
    Affected if VNC server is enabled and bound to a network interface accessible to the guest

A system is affected if it runs QEMU versions before 2.9, has the Cirrus CLGD 54xx VGA emulator enabled, and has VNC display access configured.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade QEMU to version 2.9 or later to patch this vulnerability. If immediate upgrading is not feasible, restrict VNC access to trusted guests and consider network segmentation.

Recommended fix High confidence

QEMU 2.9 or later (or vendor-supplied patches that incorporate the QEMU 2.9 security fix)

  1. Identify the QEMU version currently in use by checking the hypervisor (xe for XenServer, qemu-kvm for RHEL, etc.)
  2. For XenServer: Upgrade to a XenServer version that includes QEMU 2.9 or later, or apply XenServer security patches
  3. For Red Hat Enterprise Linux: Apply the RHSA-2017:0088 or subsequent security advisories that address CVE-2016-9603
  4. For Debian: Upgrade the qemu and qemu-kvm packages to versions that include the fix (Debian 7.12 or later)
  5. For OpenStack: Upgrade the Nova compute nodes to include the fixed QEMU version
  6. After patching, restart the libvirt/qemu services on compute hosts to load the fixed version
  7. Verify the QEMU version after upgrade to confirm it is 2.9 or later
  8. Migrate running VMs to other hosts before restarting services to avoid downtime
Caveat Virtual machines will need to be restarted or migrated after applying the QEMU update; live migration may not preserve the vulnerable QEMU process

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Xenserver Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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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-2016-9603 in production — separate from our analysis above.

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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