# CVE-2020-9991: Denial of service in iCloud for Windows

> A remote attacker can cause a denial of service in Apple operating systems and iCloud for Windows.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 Dec 2020
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-5pgw-jw9q-8cfq, UBUNTU-CVE-2020-9991

## What is CVE-2020-9991?

CVE-2020-9991 is a high-severity denial of service vulnerability in Apple Icloud, published on 8 Dec 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

This issue was addressed with improved checks. This issue is fixed in macOS Big Sur 11.0.1, watchOS 7.0, iOS 14.0 and iPadOS 14.0, iCloud for Windows 7.21, tvOS 14.0. A remote attacker may be able to cause a denial of service.

## Which versions are affected by CVE-2020-9991?

It affects 6 products.


Products: Apple Icloud, Apple Ipados, Apple Iphone Os, Apple Mac Os X, Apple Tvos, Apple Watchos.

## How do I fix CVE-2020-9991?

No fix has been published for CVE-2020-9991 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-9991 being exploited?

There is no known exploitation of CVE-2020-9991 in the wild and no public exploit code.

## Other vulnerabilities in Apple Icloud

- [CVE-2019-8506](https://insights.sbomify.com/CVE-2019-8506/): Apple Multiple Products Type Confusion (high 8.8, exploited in the wild)
- [CVE-2020-27932](https://insights.sbomify.com/CVE-2020-27932/): Apple Multiple Products Type Confusion (high 7.8, exploited in the wild)
- [CVE-2019-8746](https://insights.sbomify.com/CVE-2019-8746/): Memory corruption in iOS (critical 9.8)
- [CVE-2019-8749](https://insights.sbomify.com/CVE-2019-8749/): Memory corruption in iOS (critical 9.8)
- [CVE-2019-8756](https://insights.sbomify.com/CVE-2019-8756/): Memory corruption in iOS (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-9991 and fix it if it is affected.

What it is: CVE-2020-9991 is a high-severity denial of service vulnerability in Apple Icloud, published on 8 Dec 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2020-9991 in the wild and no public exploit code.

Affected product: Apple Icloud. 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-2020-9991/ (Markdown: https://insights.sbomify.com/CVE-2020-9991/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-9991
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-9991
- OSV: https://osv.dev/vulnerability/CVE-2020-9991

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-9991/
Summaries are generated and may contain mistakes; the official description above is the record.