CVE-2021-28705

What it is

issues with partially successful P2M updates on x86 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). In some cases the hypervisor carries out the requests by splitting them into smaller chunks. Error handling in certain PoD cases has been insufficient in that in particular partial success of some operations was not properly accounted for. There are two code paths affected - page removal (CVE-2021-28705) and insertion of new pages (CVE-2021-28709). (We provide one patch which combines the fix to both issues.)

At a glance

Exploitability

Can be exploited locally on the machine with a low-privilege account. High risk of data exposure, data tampering, service disruption.

Exploit odds

0.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-11-24 02:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:46 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.4% in the next 30 days (EPSS).
• Severity: 7.8 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-11-24 02:15 UTC

Last modified

2026-06-17 03:46 UTC

Exploit probability

0.4% · EPSS, next 30 days

Weakness

CWE-755

Record status

Modified

Affected

• Xen ≤ 4.12.4
• Xen ≤ 4.13.4
• Xen ≤ 4.14.3
• Xen 4.15.0
• Xen 4.15.1
• Fedoraproject Fedora 34
• Fedoraproject Fedora 35
• Debian Linux 11.0

Attack profile CVSS 3.1 · 7.8

Attack vector

Local

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-28705.md and follow it. Check whether this project is affected by CVE-2021-28705. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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