# CVE-2026-30867: CocoaMQTT: Denial of Service via Reachable Assertion in `PUBLISH` Packet Parsing

> A malicious MQTT broker can crash iOS/macOS apps by sending a malformed retained PUBLISH packet, causing a persistent denial of service.

- **Severity:** Medium 5.7 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 2 Apr 2026
- **Updated:** 2 Apr 2026
- **Also known as:** GHSA-r3fr-7m74-q7g2

## What is CVE-2026-30867?

CVE-2026-30867 is a medium-severity denial of service vulnerability in emqx CocoaMQTT, published on 2 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

CocoaMQTT is a MQTT 5.0 client library for iOS and macOS written in Swift. Prior to version 2.2.2, a vulnerability exists in the packet parsing logic of CocoaMQTT that allows an attacker (or a compromised/malicious MQTT broker) to remotely crash the host iOS/macOS/tvOS application. If an attacker publishes the 4-byte malformed payload to a shared topic with the RETAIN flag set to true, the MQTT broker will persist the payload. Any time a vulnerable client connects and subscribes to that topic, the broker will automatically push the malformed packet. The app will instantly crash in the background before the user can even interact with it. This effectively "bricks" the mobile application (a persistent DoS) until the retained message is manually wiped from the broker database. This issue has been patched in version 2.2.2.

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-30867?

2 open source packages ship an affected version, including CocoaMQTT. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `CocoaMQTT` | SwiftURL | All versions | 2.2.2 |
| `CocoaMQTT` | SwiftURL | All versions | 2.2.2 |

Products: Emqx Cocoamqtt.

## How do I fix CVE-2026-30867?

Upgrade CocoaMQTT to 2.2.2 or later.

## Is CVE-2026-30867 being exploited?

There is no known exploitation of CVE-2026-30867 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-30867 and fix it if it is affected.

What it is: CVE-2026-30867 is a medium-severity denial of service vulnerability in emqx CocoaMQTT, published on 2 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-30867 in the wild and no public exploit code.

Affected packages and fixed versions:
- CocoaMQTT (SwiftURL): affected all versions; fixed in 2.2.2
- CocoaMQTT (SwiftURL): affected all versions; fixed in 2.2.2

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-2026-30867/ (Markdown: https://insights.sbomify.com/CVE-2026-30867/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-30867
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-30867
- OSV: https://osv.dev/vulnerability/CVE-2026-30867

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-30867/
Summaries are generated and may contain mistakes; the official description above is the record.