# CVE-2020-29566: Denial of service in n/a

> A malicious stubdomain can trigger a stack overflow in the Xen hypervisor, causing a host-wide denial of service on x86 systems.

- **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:** 15 Dec 2020
- **Updated:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2020-29566, DEBIAN-CVE-2020-29566, GHSA-mr64-xwwr-mx4c, UBUNTU-CVE-2020-29566

## What is CVE-2020-29566?

CVE-2020-29566 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 15 Dec 2020. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

An issue was discovered in Xen through 4.14.x. When they require assistance from the device model, x86 HVM guests must be temporarily de-scheduled. The device model will signal Xen when it has completed its operation, via an event channel, so that the relevant vCPU is rescheduled. If the device model were to signal Xen without having actually completed the operation, the de-schedule / re-schedule cycle would repeat. If, in addition, Xen is resignalled very quickly, the re-schedule may occur before the de-schedule was fully complete, triggering a shortcut. This potentially repeating process uses ordinary recursive function calls, and thus could result in a stack overflow. A malicious or buggy stubdomain serving a HVM guest can cause Xen to crash, resulting in a Denial of Service (DoS) to the entire host. Only x86 systems are affected. Arm systems are not affected. Only x86 stubdomains serving HVM guests can exploit the vulnerability.

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2020-29566?

It affects 3 products.


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

## How do I fix CVE-2020-29566?

Apply the vendor's patch.

## Is CVE-2020-29566 being exploited?

There is no known exploitation of CVE-2020-29566 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)
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- [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-2020-29566 and fix it if it is affected.

What it is: CVE-2020-29566 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 15 Dec 2020. 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-2020-29566 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-2020-29566/ (Markdown: https://insights.sbomify.com/CVE-2020-29566/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-29566
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-29566
- OSV: https://osv.dev/vulnerability/CVE-2020-29566

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-29566/
Summaries are generated and may contain mistakes; the official description above is the record.