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Fencer Vulns
high 7.5

CVE-2019-18421 json

An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to gain host OS privileges by leveraging race conditions in pa…

published 2019-10-31 7 y ago modified 2026-06-17 4 mo ago also EUVD-2019-8190

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.7%
EPSS 1.7% chance of exploitation in 30 days, percentile 77%
public exploits
0
none known

Summary

An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to gain host OS privileges by leveraging race conditions in pagetable promotion and demotion operations. There are issues with restartable PV type change operations. To avoid using shadow pagetables for PV guests, Xen exposes the actual hardware pagetables to the guest. In order to prevent the guest from modifying these page tables directly, Xen keeps track of how pages are used using a type system; pages must be "promoted" before being used as a pagetable, and "demoted" before being used for any other type. Xen also allows for "recursive" promotions: i.e., an operating system promoting a page to an L4 pagetable may end up causing pages to be promoted to L3s, which may in turn cause pages to be promoted to L2s, and so on. These operations may take an arbitrarily large amount of time, and so must be re-startable. Unfortunately, making recursive pagetable promotion and demotion operations restartable is incredibly complicated, and the code contains several races which, if triggered, can cause Xen to drop or retain extra type counts, potentially allowing guests to get write access to in-use pagetables. A malicious PV guest administrator may be able to escalate their privilege to that of the host. All x86 systems with untrusted PV guests are vulnerable. HVM and PVH guests cannot exercise this vulnerability.

Patch / fix

  • xen Debian 14, Debian 13, Debian 12 4.11.3+24-g14b62ab3e5-1

debian advisories DEBIAN-CVE-2019-18421

  • xen SLE Point of Sale 11 SP3 4.2.5_22-45.36.1
  • xen SLES for SAP 12 SP2, SLES 12 SP2-LTSS, SLES 12 SP2-BCL +1 more 4.7.6_06-43.59.1
  • xen SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +4 more 4.9.4_06-3.59.1
  • xen SLES for SAP 12 SP4, SLES 12 SP4, SLED 12 SP4 +1 more 4.11.2_04-2.17.1
  • xen SLE Module for Server Applications 15 SP1, SLE Module for Basesystem 15 SP1 4.12.1_04-3.6.1
  • xen SLE Module for Server Applications 15, SLE Module for Basesystem 15 4.10.4_06-3.25.1
  • xen SLES 11 SP4-LTSS 4.4.4_42-61.52.1
  • xen SLES for SAP 12 SP1, SLES 12 SP1-LTSS 4.5.5_28-22.64.1

suse advisories SUSE-SU-2020:14448-1SUSE-SU-2020:14444-1SUSE-SU-2020:0388-1SUSE-SU-2020:0334-1SUSE-SU-2019:3297-1SUSE-SU-2019:2962-1

  • xen openSUSE Leap 15.0 4.10.4_06-lp150.2.25.1

opensuse advisories openSUSE-SU-2019:2506-1

  • xen Alpine 3.10 4.12.1-r1
  • xen Alpine 3.24, Alpine 3.23, Alpine 3.22 +11 more 4.13.0-r0
  • xen Alpine 3.8 4.10.4-r1
  • xen Alpine 3.9 4.11.2-r1

alpine advisories ALPINE-CVE-2019-18421

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2019-18421 updated cvss 8.0

xen: a malicious PV guest administrator may be able to escalate their privilege to that of the host

  • Red Hat Enterprise Linux 5 kernel-xen
    affected: no fix planned “Out of support scope”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.68% chance of exploitation in the next 30 days, higher than 77% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.1 AV:N/AC:H/Au:S/C:C/I:C/A:C

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.