# CVE-2026-42255: Denial of service in DnsServer

> Attackers can cause DNS traffic amplification and denial of service via cyclic name server delegation in Technitium DNS Server.

- **Severity:** High 7.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/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:** 26 Apr 2026
- **Updated:** 27 Apr 2026
- **Also known as:** GHSA-v7f3-6mf2-m8hj

## What is CVE-2026-42255?

CVE-2026-42255 is a high-severity denial of service vulnerability in Technitium DnsServer, published on 26 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Technitium DNS Server before 15.0 allows DNS traffic amplification via cyclic name server delegation.

Weakness: CWE-684 (Incorrect Provision of Specified Functionality)

## Which versions are affected by CVE-2026-42255?

It affects 1 product.


Products: Technitium Dnsserver.

## How do I fix CVE-2026-42255?

No fix has been published for CVE-2026-42255 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-42255 being exploited?

There is no known exploitation of CVE-2026-42255 in the wild and no public exploit code.

## Other vulnerabilities in Technitium DnsServer

- [CVE-2025-50334](https://insights.sbomify.com/CVE-2025-50334/): Denial of service in n/a (high 7.5)
- [CVE-2024-56089](https://insights.sbomify.com/CVE-2024-56089/): Other in n/a (high 7.5)
- [CVE-2023-28451](https://insights.sbomify.com/CVE-2023-28451/): Denial of service in n/a (high 7.5)
- [CVE-2023-28455](https://insights.sbomify.com/CVE-2023-28455/): Denial of service in n/a (high 7.5)
- [CVE-2023-28456](https://insights.sbomify.com/CVE-2023-28456/): Denial of service in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42255 and fix it if it is affected.

What it is: CVE-2026-42255 is a high-severity denial of service vulnerability in Technitium DnsServer, published on 26 Apr 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-2026-42255 in the wild and no public exploit code.

Affected product: Technitium DnsServer. 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-2026-42255/ (Markdown: https://insights.sbomify.com/CVE-2026-42255/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42255
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42255
- OSV: https://osv.dev/vulnerability/CVE-2026-42255

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42255/
Summaries are generated and may contain mistakes; the official description above is the record.