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Fencer Vulns
high 8.8

CVE-2021-28704 json

PoD operations on misaligned GFNs T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities co…

published 2021-11-24 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-15361

cvss
8.8
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 29%
public exploits
0
none known

Summary

PoD operations on misaligned GFNs T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] x86 HVM and PVH guests may be started in populate-on-demand (PoD) mode, to provide a way for them to later easily have more memory assigned. Guests are permitted to control certain P2M aspects of individual pages via hypercalls. These hypercalls may act on ranges of pages specified via page orders (resulting in a power-of-2 number of pages). The implementation of some of these hypercalls for PoD does not enforce the base page frame number to be suitably aligned for the specified order, yet some code involved in PoD handling actually makes such an assumption. These operations are XENMEM_decrease_reservation (CVE-2021-28704) and XENMEM_populate_physmap (CVE-2021-28707), the latter usable only by domains controlling the guest, i.e. a de-privileged qemu or a stub domain. (Patch 1, combining the fix to both these two issues.) In addition handling of XENMEM_decrease_reservation can also trigger a host crash when the specified page order is neither 4k nor 2M nor 1G (CVE-2021-28708, patch 2).

Patch / fix

  • xen Debian 14, Debian 13, Debian 12 4.14.3+32-g9de3671772-1

debian advisories DEBIAN-CVE-2021-28704

  • xen SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +3 more 4.12.4_16-3.57.1
  • xen SLE Module for Server Applications 15 SP3, SLE Module for Basesystem 15 SP3, SLE Micro 5.1 4.14.3_04-3.15.1
  • xen SLE Module for Server Applications 15 SP2, SLE Module for Basesystem 15 SP2, SLE Micro 5.0 4.13.4_02-3.40.1
  • xen SLES for SAP 12 SP5, SLES 12 SP5, SLE Software Development Kit 12 SP5 4.12.4_16-3.55.1
  • xen SLES for SAP 12 SP3, SLES 12 SP3-LTSS, SLES 12 SP3-BCL +3 more 4.9.4_24-3.97.1
  • xen SLES for SAP 12 SP4, SLES 12 SP4-LTSS, OpenStack Cloud Crowbar 9 +1 more 4.11.4_24-2.65.1
  • xen SLES for SAP 15, SLE High Performance Computing 15-LTSS, SLE High Performance Computing 15-ESPOS 4.10.4_30-3.68.1
  • xen SLES 12 SP2-BCL 4.7.6_18-43.82.1

suse advisories SUSE-SU-2021:3977-1SUSE-SU-2021:3968-1SUSE-SU-2021:3888-1SUSE-SU-2021:3852-1SUSE-SU-2021:3851-1SUSE-SU-2021:3849-1

  • xen openSUSE Leap 15.3 4.14.3_04-3.15.1
  • xen openSUSE Leap 15.2 4.13.4_02-lp152.2.33.1

opensuse advisories openSUSE-SU-2021:3968-1openSUSE-SU-2021:1543-1

  • xen Alpine 3.12, Alpine 3.11 4.13.4-r2
  • xen Alpine 3.13 4.14.3-r2
  • xen Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 4.15.1-r2

alpine advisories ALPINE-CVE-2021-28704

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

Exploit prediction

0.35% chance of exploitation in the next 30 days, higher than 29% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 8.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
NVD 2.0 6.9 AV:L/AC:M/Au:N/C:C/I:C/A:C

Affected products

  • Xen xen

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.