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Fencer Intel
medium 6.5

CVE-2019-18420 json

An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to cause a denial of service via a VCPUOP_initialise hypercall.

published 7y ago modified 4mo ago also EUVD-2019-8189

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
2.9%
EPSS 2.9% chance of exploitation in 30 days, percentile 87%
public exploits
0
none known

Summary

An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to cause a denial of service via a VCPUOP_initialise hypercall. hypercall_create_continuation() is a variadic function which uses a printf-like format string to interpret its parameters. Error handling for a bad format character was done using BUG(), which crashes Xen. One path, via the VCPUOP_initialise hypercall, has a bad format character. The BUG() can be hit if VCPUOP_initialise executes for a sufficiently long period of time for a continuation to be created. Malicious guests may cause a hypervisor crash, resulting in a Denial of Service (DoS). Xen versions 4.6 and newer are vulnerable. Xen versions 4.5 and earlier are not vulnerable. Only x86 PV guests can exploit the vulnerability. HVM and PVH guests, and guests on ARM systems, cannot exploit the vulnerability.

Patch / fix

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

debian advisories DEBIAN-CVE-2019-18420

  • 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-2020:14444-1SUSE-SU-2020:0388-1SUSE-SU-2020:0334-1SUSE-SU-2019:3297-1SUSE-SU-2019:2962-1SUSE-SU-2019:2961-1

  • xen openSUSE Leap 15.0 4.10.4_06-lp150.2.25.1

opensuse advisories openSUSE-SU-2019:2506-1

  • xen Alpine 3.9 4.11.2-r0

alpine advisories ALPINE-CVE-2019-18420

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

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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-2019-18420 updated cvss 7.4

xen: allows guest OS users to cause denial of service via VCPUOP_initialise hypercall

  • Red Hat Enterprise Linux 5 kernel-xen
    not affected: vulnerable code not present

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

2.91% chance of exploitation in the next 30 days, higher than 87% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 6.3 AV:N/AC:M/Au:S/C:N/I:N/A:C

Classification

Weakness
  • CWE-134 Use of Externally-Controlled Format String

References

Sources

Fencer Intel 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.