# CVE-2026-43678: Denial of service in swift-nio

> An unauthenticated remote attacker can crash NIOWebSocket-based servers by sending a specific 11-byte frame, requiring developers to upgrade swift-nio.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 20 Aug 2026
- **Updated:** 20 Aug 2026
- **Also known as:** GHSA-qcc5-f287-vgmq

## What is CVE-2026-43678?

CVE-2026-43678 is a medium-severity denial of service vulnerability in Apple swift-nio, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An unauthenticated remote peer can crash any NIOWebSocket-based server (including Vapor and Hummingbird) with a single 11-byte frame sent after a completed WebSocket handshake, dropping all active connections until the process restarts. This vulnerability is addressed in swift-nio version 2.101.0.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-43678?

It affects 1 product.


Products: Apple Swiftnio.

## How do I fix CVE-2026-43678?

No fix has been published for CVE-2026-43678 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-43678 being exploited?

There is no known exploitation of CVE-2026-43678 in the wild and no public exploit code.

## Other vulnerabilities in Apple swift-nio

- [CVE-2018-4281](https://insights.sbomify.com/CVE-2018-4281/): Memory corruption in n/a (critical 9.8)
- [CVE-2022-3215](https://insights.sbomify.com/CVE-2022-3215/): SwiftNIO vulnerable to Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Response Splitting') (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43678 and fix it if it is affected.

What it is: CVE-2026-43678 is a medium-severity denial of service vulnerability in Apple swift-nio, published on 20 Aug 2026. 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-2026-43678 in the wild and no public exploit code.

Affected product: Apple swift-nio. 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-2026-43678/ (Markdown: https://insights.sbomify.com/CVE-2026-43678/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43678
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43678
- OSV: https://osv.dev/vulnerability/CVE-2026-43678

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43678/
Summaries are generated and may contain mistakes; the official description above is the record.