# CVE-2021-28694: Privilege escalation in xen

> Guests can bypass IOMMU identity mappings to access restricted memory, leading to privilege escalation and data exposure in Xen hypervisors.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Aug 2021
- **Updated:** 3 Aug 2024
- **Also known as:** ALPINE-CVE-2021-28694, DEBIAN-CVE-2021-28694, GHSA-7h6m-rq82-825p, UBUNTU-CVE-2021-28694

## What is CVE-2021-28694?

CVE-2021-28694 is a medium-severity vulnerability in Debian Debian Linux, published on 27 Aug 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Both AMD and Intel allow ACPI tables to specify regions of memory which should be left untranslated, which typically means these addresses should pass the translation phase unaltered. While these are typically device specific ACPI properties, they can also be specified to apply to a range of devices, or even all devices. On all systems with such regions Xen failed to prevent guests from undoing/replacing such mappings (CVE-2021-28694). On AMD systems, where a discontinuous range is specified by firmware, the supposedly-excluded middle range will also be identity-mapped (CVE-2021-28695). Further, on AMD systems, upon de-assigment of a physical device from a guest, the identity mappings would be left in place, allowing a guest continued access to ranges of memory which it shouldn't have access to anymore (CVE-2021-28696).

## Which versions are affected by CVE-2021-28694?

It affects 3 products.


Products: Debian Debian Linux, Fedoraproject Fedora, Xen Xen.

## How do I fix CVE-2021-28694?

Apply the vendor's patch.

## Is CVE-2021-28694 being exploited?

There is no known exploitation of CVE-2021-28694 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-28694 and fix it if it is affected.

What it is: CVE-2021-28694 is a medium-severity vulnerability in Debian Debian Linux, published on 27 Aug 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-28694 in the wild and no public exploit code.

Affected product: Debian Debian Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-28694/ (Markdown: https://insights.sbomify.com/CVE-2021-28694/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-28694
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-28694
- OSV: https://osv.dev/vulnerability/CVE-2021-28694

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-28694/
Summaries are generated and may contain mistakes; the official description above is the record.