# CVE-2021-3308: Denial of service in n/a

> A malicious HVM guest with PCI pass-through can exhaust system IDT vectors, causing a denial of service for other guests or the host.

- **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:** 26 Jan 2021
- **Updated:** 3 Aug 2024
- **Also known as:** ALPINE-CVE-2021-3308, DEBIAN-CVE-2021-3308, GHSA-4gx5-7c23-79mh

## What is CVE-2021-3308?

CVE-2021-3308 is a medium-severity denial of service vulnerability in Fedoraproject Fedora, published on 26 Jan 2021. 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 4.12.3 through 4.12.4 and 4.13.1 through 4.14.x. An x86 HVM guest with PCI pass through devices can force the allocation of all IDT vectors on the system by rebooting itself with MSI or MSI-X capabilities enabled and entries setup. Such reboots will leak any vectors used by the MSI(-X) entries that the guest might had enabled, and hence will lead to vector exhaustion on the system, not allowing further PCI pass through devices to work properly. HVM guests with PCI pass through devices can mount a Denial of Service (DoS) attack affecting the pass through of PCI devices to other guests or the hardware domain. In the latter case, this would affect the entire host.

## Which versions are affected by CVE-2021-3308?

It affects 2 products.


Products: Fedoraproject Fedora, Xen Xen.

## How do I fix CVE-2021-3308?

Apply the vendor's patch.

## Is CVE-2021-3308 being exploited?

There is no known exploitation of CVE-2021-3308 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3308 and fix it if it is affected.

What it is: CVE-2021-3308 is a medium-severity denial of service vulnerability in Fedoraproject Fedora, published on 26 Jan 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-2021-3308 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. 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-2021-3308/ (Markdown: https://insights.sbomify.com/CVE-2021-3308/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3308
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3308
- OSV: https://osv.dev/vulnerability/CVE-2021-3308

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3308/
Summaries are generated and may contain mistakes; the official description above is the record.