Skip to content
Fencer Vulns
high 7.8

CVE-2020-25603 json

An issue was discovered in Xen through 4.14.x.

published 2020-09-23 6 y ago modified 2026-06-17 4 mo ago also EUVD-2020-18282

cvss
7.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 36%
public exploits
0
none known

Summary

An issue was discovered in Xen through 4.14.x. There are missing memory barriers when accessing/allocating an event channel. Event channels control structures can be accessed lockless as long as the port is considered to be valid. Such a sequence is missing an appropriate memory barrier (e.g., smp_*mb()) to prevent both the compiler and CPU from re-ordering access. A malicious guest may be able to cause a hypervisor crash resulting in a Denial of Service (DoS). Information leak and privilege escalation cannot be excluded. Systems running all versions of Xen are affected. Whether a system is vulnerable will depend on the CPU and compiler used to build Xen. For all systems, the presence and the scope of the vulnerability depend on the precise re-ordering performed by the compiler used to build Xen. We have not been able to survey compilers; consequently we cannot say which compiler(s) might produce vulnerable code (with which code generation options). GCC documentation clearly suggests that re-ordering is possible. Arm systems will also be vulnerable if the CPU is able to re-order memory access. Please consult your CPU vendor. x86 systems are only vulnerable if a compiler performs re-ordering.

Patch / fix

  • xen Debian 14, Debian 13, Debian 12 4.14.0+80-gd101b417b7-1

debian advisories DEBIAN-CVE-2020-25603

  • xen Ubuntu 20.04 LTS 4.11.3+24-g14b62ab3e5-1ubuntu2.3

ubuntu advisories UBUNTU-CVE-2020-25603

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • xen SLES for SAP 12 SP2, SLES 12 SP2-LTSS, SLES 12 SP2-BCL +1 more 4.7.6_10-43.67.1
  • xen SLE Module for Server Applications 15 SP2, SLE Module for Basesystem 15 SP2 4.13.1_08-3.10.1
  • xen SLE Module for Server Applications 15 SP1, SLE Module for Basesystem 15 SP1 4.12.3_08-3.28.1
  • xen SLES for SAP 15, SLE High Performance Computing 15-LTSS, SLE High Performance Computing 15-ESPOS 4.10.4_16-3.41.1
  • xen SLES for SAP 12 SP5, SLES 12 SP5, SLE Software Development Kit 12 SP5 4.12.3_08-3.24.1
  • xen SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +4 more 4.9.4_12-3.74.1
  • xen SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 4.11.4_08-2.36.1
  • xen SLES 11 SP4-LTSS 4.4.4_44-61.55.1

suse advisories SUSE-SU-2020:14521-1SUSE-SU-2020:2822-1SUSE-SU-2020:2791-1SUSE-SU-2020:2790-1SUSE-SU-2020:2789-1SUSE-SU-2020:2788-1

  • xen openSUSE Tumbleweed 4.15.1_01-1.2
  • xen openSUSE Leap 15.2 4.13.1_08-lp152.2.9.1

opensuse advisories openSUSE-SU-2024:11520-1openSUSE-SU-2020:1608-1

  • xen Alpine 3.10 4.12.3-r4
  • xen Alpine 3.12, Alpine 3.11 4.13.1-r4
  • xen Alpine 3.24, Alpine 3.23, Alpine 3.22 +9 more 4.14.0-r1
  • xen Alpine 3.9 4.11.4-r2

alpine advisories ALPINE-CVE-2020-25603

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-2020-25603 updated cvss 7.0

xen: missing memory barriers when accessing/allocating an event channel (XSA-340)

  • Red Hat Enterprise Linux 5 kernel-xen
    affected: workaround, no fix planned “There is no known mitigation for this flaw apart from applying the patch.”

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

0.41% chance of exploitation in the next 30 days, higher than 36% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 4.6 AV:L/AC:L/Au:N/C:P/I:P/A:P

Classification

Weakness
  • CWE-670 Always-Incorrect Control Flow Implementation

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.