# CVE-2025-56352: Denial of service in n/a

> An attacker can cause denial of service in the tinyMQTT broker by sending repeated invalid CONNECT packets that leak file descriptors and memory.

- **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:** 18 May 2026
- **Updated:** 18 May 2026
- **Also known as:** GHSA-m5jh-ppcv-76xr

## What is CVE-2025-56352?

CVE-2025-56352 is a high-severity denial of service vulnerability in n/a, published on 18 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In tinyMQTT commit 6226ade15bd4f97be2d196352e64dd10937c1962 (2024-02-18), the broker mishandles protocol violations during CONNECT packet parsing. When receiving a CONNECT packet with a zero-length Client ID while CleanSession is set to 0, the broker correctly replies with a CONNACK return code 0x02 (Identifier Rejected) but fails to explicitly close the TCP connection. Since the surrounding connection teardown logic is not guaranteed to execute, each such invalid CONNECT attempt leaves the underlying socket open. Repeated attempts cause server-side resource exhaustion due to accumulating file descriptors and memory usage, potentially resulting in denial of service.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2025-56352?


## How do I fix CVE-2025-56352?

No fix has been published for CVE-2025-56352 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-56352 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-56352 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-56352 and fix it if it is affected.

What it is: CVE-2025-56352 is a high-severity denial of service vulnerability in n/a, published on 18 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-56352 exists.

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-2025-56352/ (Markdown: https://insights.sbomify.com/CVE-2025-56352/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-56352
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-56352
- OSV: https://osv.dev/vulnerability/CVE-2025-56352

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-56352/
Summaries are generated and may contain mistakes; the official description above is the record.