CVE-2015-4104
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 · uneditedXen 3.3.x through 4.5.x does not properly restrict access to PCI MSI mask bits, which allows local x86 HVM guest users to cause a denial of service (unexpected interrupt and host crash) via unspecified vectors.
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 confidenceXen 3.3.x through 4.5.x fails to properly restrict access to PCI MSI (Message Signaled Interrupts) mask bits. Local x86 HVM guest users can manipulate these MSI mask bits to trigger unexpected interrupts, causing a denial of service via host crash.
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= 3.3.0= 3.3.1= 3.3.2= 3.4.0= 3.4.1= 3.4.2= 3.4.3= 3.4.4= 4.0.0= 4.0.1= 4.0.2= 4.0.3CVSS 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
- Authentication
- None
- Confidentiality
- None
- Integrity
- None
- Availability
- Complete
AV:N/AC:L/Au:N/C:N/I:N/A:C
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 checksWork through these to decide whether this CVE applies to you.
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Identify Xen hypervisor versionRun 'xl info' or 'xm info' to display hypervisor information, or check the Xen package version with 'rpm -q xen' or 'dpkg -l xen-common' depending on your Linux distributionAffected if The displayed Xen version is 3.3.0 through 3.4.4, 4.0.0 through 4.0.3, or any 4.1.x through 4.5.x version (if your version falls within 3.3.x to 4.5.x, you are in the affected range)
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Confirm HVM guest usageList all virtual machines with 'xl list' or 'xm list' and identify any guests with type 'hvm'Affected if Any HVM (Hardware Virtual Machine) guests are running on the Xen host
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Check for PCI device assignment to HVM guestsRun 'xl pci-list <guest_name>' for each HVM guest to see assigned PCI devices, or use 'lspci' within the guest to identify PCI devices with MSI capabilityAffected if HVM guests have assigned PCI devices that support MSI (Message Signaled Interrupts)
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Verify MSI mask bit accessibilityInspect the hypervisor configuration in /etc/xen/xend-config.sxp (or xl.conf) for PCI device assignment settings, and check if the qemu-dm or qemu process for HVM guests has direct access to PCI MSI registersAffected if PCI devices with MSI capability are directly assigned to untrusted HVM guests without additional isolation
Your environment is affected if you are running a Xen version between 3.3.0 and 4.5.x with HVM guests that have PCI devices with MSI capabilities assigned to them.
Generated from the published advisory. Verify against your own configuration.
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 dataUpgrade Xen to a version that properly restricts PCI MSI mask bit access. In the interim, minimize risk by avoiding assignment of PCI devices with MSI capabilities to untrusted HVM guests.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,176.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2015-4104 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sources- xenbits.xen.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.fedoraproject.org
- lists.opensuse.org
- lists.opensuse.org
- lists.opensuse.org
- lists.opensuse.org
- support.citrix.com
- www.debian.org
- www.debian.org
- www.securityfocus.com
- www.securitytracker.com
- www.ubuntu.com
- security.gentoo.org
- support.citrix.com
- nvd.nist.gov
Practitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2015-4104 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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