# CVE-2025-56353: Denial of service in n/a

> An attacker can cause denial of service in tinyMQTT by sending malformed UTF-8 topic filters that trigger unbounded memory allocation.

- **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:** 20 Jan 2026
- **Updated:** 21 Jan 2026
- **Also known as:** GHSA-cqjp-pfhx-4jwv

## What is CVE-2025-56353?

CVE-2025-56353 is a high-severity denial of service vulnerability in n/a, published on 20 Jan 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), a memory leak occurs due to the broker's failure to validate or reject malformed UTF-8 strings in topic filters. An attacker can exploit this by sending repeated subscription requests with arbitrarily large or invalid filter payloads. Each request causes memory to be allocated for the malformed topic filter, but the broker does not free the associated memory, leading to unbounded heap growth and potential denial of service under sustained attack.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2025-56353?

It affects 1 product.


Products: Justdoit0910 Tinymqtt.

## How do I fix CVE-2025-56353?

No fix has been published for CVE-2025-56353 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-56353 being exploited?

There is no known exploitation of CVE-2025-56353 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-56353 and fix it if it is affected.

What it is: CVE-2025-56353 is a high-severity denial of service vulnerability in n/a, published on 20 Jan 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-2025-56353 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-2025-56353/ (Markdown: https://insights.sbomify.com/CVE-2025-56353/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-56353
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-56353
- OSV: https://osv.dev/vulnerability/CVE-2025-56353

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-56353/
Summaries are generated and may contain mistakes; the official description above is the record.