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FedoraOperating system · Fedoraproject

CVE-2019-19579

MEDIUM · 6.8 CVSS v3.1 Published 2019-12-04
Fix available
A fix is available. Upgrade to after 4.12.1 or later.
See remediation →
73/100
Remediation priority · Elevated
No privileges 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
An issue was discovered in Xen through 4.12.x allowing attackers to gain host OS privileges via DMA in a situation where an untrusted domain has access to a physical device (and assignable-add is not used), because of an incomplete fix for CVE-2019-18424. XSA-302 relies on the use of libxl's "assignable-add" feature to prepare devices to be assigned to untrusted guests. Unfortunately, this is not considered a strictly required step for device assignment. The PCI passthrough documentation on the wiki describes alternate ways of preparing devices for assignment, and libvirt uses its own ways as well. Hosts where these "alternate" methods are used will still leave the system in a vulnerable state after the device comes back from a guest. An untrusted domain with access to a physical device can DMA into host memory, leading to privilege escalation. Only systems where guests are given direct access to physical devices capable of DMA (PCI pass-through) are vulnerable. Systems which do not use PCI pass-through are not vulnerable.

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

Xen through 4.12.x contains an incomplete fix for CVE-2019-18424 (XSA-302). The original fix relied on libxl's 'assignable-add' feature to secure devices before passthrough, but alternate preparation methods (used by libvirt and documented on the wiki) leave systems vulnerable. An untrusted domain with access to a physical device capable of DMA can perform DMA attacks into host memory, achieving privilege escalation to the host OS.

MitigationDisable PCI passthrough for untrusted guests if not strictly required; if needed, ensure proper device isolation mechanisms are in place and consider applying Xen security patches when available. Systems without PCI passthrough are not vulnerable.

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
FedoraOperating system
Affected:= 30
XenOperating system
Affected:<= 4.12.1

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

CVSS:3.1/AV:P/AC:L/PR:N/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. Check Xen hypervisor version
    Run 'xl version' or 'xm version' to obtain the installed Xen version number
    Affected if The version is 4.12.1 or lower (any version up to and including 4.12.1)
  2. Verify PCI passthrough is enabled in the hypervisor
    Check for 'passthrough' or 'pci' settings in /etc/xen/xl.conf and examine xl config files for 'pci' device assignments with 'seize' option or similar PCI device assignment directives
    Affected if PCI passthrough is actively configured and assigned to any guest domain
  3. Identify domains with assigned PCI devices capable of DMA
    Run 'xl pci-list <domain>' for each domain to list assigned PCI devices. Focus on devices that support DMA (common examples include network cards, storage controllers, GPUs)
    Affected if Any untrusted or less-trusted guest domain has a PCI device with DMA capability directly assigned
  4. Check how device assignment was prepared
    Review system documentation or scripts used to prepare devices for passthrough. Verify whether libxl's 'assignable-add' feature was used versus alternate methods (such as manual device preparation via libvirt or wiki-documented methods)
    Affected if Devices were prepared using methods other than libxl's native 'assignable-add' workflow, leaving the incomplete fix bypassed
  5. Assess trust level of PCI-passthrough-enabled guests
    Review domain configurations and determine which guests with PCI passthrough are considered untrusted or less trusted (such as horizontally-shared tenants, demo systems, or domains running third-party code)
    Affected if Any untrusted guest domain has direct access to a physical PCI device capable of DMA operations

A system is affected if it runs Xen 4.12.1 or lower AND has untrusted guest domains with directly assigned PCI devices that support DMA, particularly when devices were prepared using methods other than libxl's native assignable-add feature.

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
Upgrade available Upgrade to a release after 4.12.1
Interim mitigation

Disable PCI passthrough for untrusted guests if not strictly required; if needed, ensure proper device isolation mechanisms are in place and consider applying Xen security patches when available. Systems without PCI passthrough are not vulnerable.

Fix this in Fedora Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
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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-2019-19579 in production — separate from our analysis above.

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What this is

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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