# CVE-2020-9861: Denial of service in Swift 5.1.5 for Linux

> Attackers can cause a stack overflow and denial of service in Swift for Linux by providing deeply nested malicious JSON input.

- **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:** 2 Nov 2020
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-g4pr-mpxh-7vhq

## What is CVE-2020-9861?

CVE-2020-9861 is a high-severity denial of service vulnerability in Swift 5.1.5 for Linux, published on 2 Nov 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A stack overflow issue existed in Swift for Linux. The issue was addressed with improved input validation for dealing with deeply nested malicious JSON input.

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2020-9861?

It affects 1 product.


Products: Apple Swift.

## How do I fix CVE-2020-9861?

No fix has been published for CVE-2020-9861 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-9861 being exploited?

There is no known exploitation of CVE-2020-9861 in the wild and no public exploit code.

## Other vulnerabilities in Swift 5.1.5 for Linux

- [CVE-2018-4220](https://insights.sbomify.com/CVE-2018-4220/): Privilege escalation in n/a (high 8.8)
- [CVE-2022-1642](https://insights.sbomify.com/CVE-2022-1642/): Swift-corelibs-foundation denial of service in JSON decoding with JSONDecoder (high 7.5)
- [CVE-2019-8790](https://insights.sbomify.com/CVE-2019-8790/): Information disclosure in Swift for Ubuntu (medium 5.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-9861 and fix it if it is affected.

What it is: CVE-2020-9861 is a high-severity denial of service vulnerability in Swift 5.1.5 for Linux, published on 2 Nov 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-2020-9861 in the wild and no public exploit code.

Affected product: Swift 5.1.5 for 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-2020-9861/ (Markdown: https://insights.sbomify.com/CVE-2020-9861/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-9861
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-9861
- OSV: https://osv.dev/vulnerability/CVE-2020-9861

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-9861/
Summaries are generated and may contain mistakes; the official description above is the record.