# CVE-2021-28698: Denial of service in xen

> A malicious guest can cause a denial of service by triggering long-running loops in Xen's grant table handling, starving other domains or the hypervisor.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **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-2021-28698, DEBIAN-CVE-2021-28698, GHSA-2g34-x978-mw32, UBUNTU-CVE-2021-28698

## What is CVE-2021-28698?

CVE-2021-28698 is a medium-severity denial of service 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

long running loops in grant table handling In order to properly monitor resource use, Xen maintains information on the grant mappings a domain may create to map grants offered by other domains. In the process of carrying out certain actions, Xen would iterate over all such entries, including ones which aren't in use anymore and some which may have been created but never used. If the number of entries for a given domain is large enough, this iterating of the entire table may tie up a CPU for too long, starving other domains or causing issues in the hypervisor itself. Note that a domain may map its own grants, i.e. there is no need for multiple domains to be involved here. A pair of "cooperating" guests may, however, cause the effects to be more severe.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2021-28698?

It affects 3 products.


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

## How do I fix CVE-2021-28698?

Apply the vendor's patch.

## Is CVE-2021-28698 being exploited?

There is no known exploitation of CVE-2021-28698 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-2021-28698 and fix it if it is affected.

What it is: CVE-2021-28698 is a medium-severity denial of service 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-2021-28698 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-2021-28698/ (Markdown: https://insights.sbomify.com/CVE-2021-28698/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-28698
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-28698
- OSV: https://osv.dev/vulnerability/CVE-2021-28698

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-28698/
Summaries are generated and may contain mistakes; the official description above is the record.