Vulnerability · Published Nov 24, 2021 · Assigned by XEN
CVE-2021-28704
High 8.8
In plain English
A high-severity security flaw in xen from Xen. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 29% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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).
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.20 | xen | 4.15.1-r2 | ALPINE-CVE-2021-28704 |
| Alpine:v3.21 | xen | 4.15.1-r2 | ALPINE-CVE-2021-28704 |
| Alpine:v3.22 | xen | 4.15.1-r2 | ALPINE-CVE-2021-28704 |
| Alpine:v3.23 | xen | 4.15.1-r2 | ALPINE-CVE-2021-28704 |
| Alpine:v3.24 | xen | 4.15.1-r2 | ALPINE-CVE-2021-28704 |
| Debian:12 | xen | 4.14.3+32-g9de3671772-1 | DEBIAN-CVE-2021-28704 |
| Debian:13 | xen | 4.14.3+32-g9de3671772-1 | DEBIAN-CVE-2021-28704 |
| Debian:14 | xen | 4.14.3+32-g9de3671772-1 | DEBIAN-CVE-2021-28704 |
| Ubuntu:22.04:LTS | xen | no fix listed | UBUNTU-CVE-2021-28704 |
| Ubuntu:24.04:LTS | xen | no fix listed | UBUNTU-CVE-2021-28704 |
| Ubuntu:25.10 | xen | no fix listed | UBUNTU-CVE-2021-28704 |
| Ubuntu:26.04:LTS | xen | no fix listed | UBUNTU-CVE-2021-28704 |
| Ubuntu:26.10 | xen | no fix listed | UBUNTU-CVE-2021-28704 |
Affected products (as reported)
References
- https://xenbits.xenproject.org/xsa/advisory-388.txt
- FEDORA-2021-03645e9807 vendor-advisory
- DSA-5017 vendor-advisory
- FEDORA-2021-2b3a2de94f vendor-advisory
- GLSA-202402-07 vendor-advisory