# CVE-2021-42143: Denial of service in n/a

> Remote attackers can cause denial of service and disclose sensitive information by sending malformed ClientHello messages to Contiki-NG tinyDTLS.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:** 24 Jan 2024
- **Updated:** 20 Jun 2025
- **Also known as:** GHSA-23p4-xxgc-xqvf

## What is CVE-2021-42143?

CVE-2021-42143 is a critical denial of service vulnerability in n/a, published on 24 Jan 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An issue was discovered in Contiki-NG tinyDTLS through master branch 53a0d97. An infinite loop bug exists during the handling of a ClientHello handshake message. This bug allows remote attackers to cause a denial of service by sending a malformed ClientHello handshake message with an odd length of cipher suites, which triggers an infinite loop (consuming all resources) and a buffer over-read that can disclose sensitive information.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2021-42143?

It affects 1 product.


Products: Contiki-Ng Tinydtls.

## How do I fix CVE-2021-42143?

No fix has been published for CVE-2021-42143 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-42143 being exploited?

There is no known exploitation of CVE-2021-42143 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2021-42147](https://insights.sbomify.com/CVE-2021-42147/): Denial of service in n/a (critical 9.1)
- [CVE-2021-42142](https://insights.sbomify.com/CVE-2021-42142/): Denial of service in n/a (high 8.2)
- [CVE-2021-42145](https://insights.sbomify.com/CVE-2021-42145/): Denial of service in n/a (high 7.5)
- [CVE-2021-42146](https://insights.sbomify.com/CVE-2021-42146/): Information disclosure in n/a (high 7.5)
- [CVE-2021-42141](https://insights.sbomify.com/CVE-2021-42141/): Denial of service in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-42143 and fix it if it is affected.

What it is: CVE-2021-42143 is a critical denial of service vulnerability in n/a, published on 24 Jan 2024. 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-2021-42143 in the wild and no public exploit code.

Affected product: n/a. 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-2021-42143/ (Markdown: https://insights.sbomify.com/CVE-2021-42143/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-42143
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-42143
- OSV: https://osv.dev/vulnerability/CVE-2021-42143

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-42143/
Summaries are generated and may contain mistakes; the official description above is the record.