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Debian LinuxOperating system · Debian

CVE-2019-18425

CRITICAL · 9.8 CVSS v3.1 Published 2019-10-31
Fix available
A fix is available. Upgrade to after 4.12.1 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available

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 32-bit PV guest OS users to gain guest OS privileges by installing and using descriptors. There is missing descriptor table limit checking in x86 PV emulation. When emulating certain PV guest operations, descriptor table accesses are performed by the emulating code. Such accesses should respect the guest specified limits, unless otherwise guaranteed to fail in such a case. Without this, emulation of 32-bit guest user mode calls through call gates would allow guest user mode to install and then use descriptors of their choice, as long as the guest kernel did not itself install an LDT. (Most OSes don't install any LDT by default). 32-bit PV guest user mode can elevate its privileges to that of the guest kernel. Xen versions from at least 3.2 onwards are affected. Only 32-bit PV guest user mode can leverage this vulnerability. HVM, PVH, as well as 64-bit PV guests cannot leverage this vulnerability. Arm systems are unaffected.

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
How this class of weakness works · CWE-269

Privileges are granted, or fail to be dropped, incorrectly, so an action runs with more power than it should. An attacker who reaches that path inherits the excess privilege. The fix is least-privilege throughout, with explicit, checked transitions whenever privilege changes.

General guidance for the improper privilege management class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

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
Debian LinuxOperating system
Affected:= 9.0= 10.0
FedoraOperating system
Affected:= 29= 30= 31
XenOperating system
Affected:<= 4.12.1
LeapOperating system
Affected:= 15.0

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

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

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
Upgrade available Upgrade to a release after 4.12.1
Vendor patch xenbits.xen.org →
Recommended fix High confidence

Xen 4.13.0 or later (or vendor-supplied patched version for 4.12.x)

  1. Identify all Xen hosts running version 4.12.1 or earlier in your infrastructure
  2. Schedule maintenance window for hypervisor updates
  3. For Debian systems: Run 'apt-get update && apt-get upgrade' or 'apt-get dist-upgrade' to apply Xen security updates
  4. For Fedora systems: Run 'dnf update' to apply Xen security updates
  5. For openSUSE Leap: Run 'zypper update' to apply Xen security updates
  6. Alternatively, upgrade Xen hypervisor to version 4.13.0 or later which contains the fix for XSA-298
  7. After updating, verify Xen version with 'xl version' or 'xm version'
  8. Ensure no 32-bit PV guests are running in production; if required, migrate to 64-bit PV, PVH, or HVM mode
Caveat Upgrading Xen hypervisor requires host reboots; ensure guest VMs are properly migrated or shut down. Some very old guest operating systems may only support 32-bit PV mode which would no longer be safe to run.

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

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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-2019-18425 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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