# CVE-2020-29571: Null dereference in n/a

> A malicious guest kernel can cause a NULL pointer dereference in the Xen hypervisor on Arm systems, leading to a system-wide Denial of Service.

- **Severity:** Medium 6.2 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 15 Dec 2020
- **Updated:** 4 Aug 2024
- **Also known as:** ALPINE-CVE-2020-29571, DEBIAN-CVE-2020-29571, GHSA-26rg-mq58-rxvm, UBUNTU-CVE-2020-29571

## What is CVE-2020-29571?

CVE-2020-29571 is a medium-severity 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. A bounds check common to most operation time functions specific to FIFO event channels depends on the CPU observing consistent state. While the producer side uses appropriately ordered writes, the consumer side isn't protected against re-ordered reads, and may hence end up de-referencing a NULL pointer. Malicious or buggy guest kernels can mount a Denial of Service (DoS) attack affecting the entire system. Only Arm systems may be vulnerable. Whether a system is vulnerable depends on the specific CPU. x86 systems are not vulnerable.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2020-29571?

It affects 3 products.


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

## How do I fix CVE-2020-29571?

Apply the vendor's patch.

## Is CVE-2020-29571 being exploited?

There is no known exploitation of CVE-2020-29571 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-2020-29571 and fix it if it is affected.

What it is: CVE-2020-29571 is a medium-severity 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-2020-29571 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-2020-29571/ (Markdown: https://insights.sbomify.com/CVE-2020-29571/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-29571
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-29571
- OSV: https://osv.dev/vulnerability/CVE-2020-29571

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-29571/
Summaries are generated and may contain mistakes; the official description above is the record.