# CVE-2026-40622: Another 'ghost domain names' attack variant

> Attackers can extend the ghost domain window by overwriting cached NS records, bypassing DNS security controls in Unbound.

- **Severity:** Medium 6.6 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Amber`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 May 2026
- **Updated:** 20 May 2026
- **Also known as:** ALPINE-CVE-2026-40622, AZL-87035, CLSA-2026-1780319730, CLSA-2026-1780479714, DEBIAN-CVE-2026-40622, ECHO-627e-e177-a81b, GHSA-m3vq-fgh9-hq65, ROOT-OS-DEBIAN-11-CVE-2026-40622, UBUNTU-CVE-2026-40622

## What is CVE-2026-40622?

CVE-2026-40622 is a medium-severity vulnerability in Nlnetlabs Unbound, published on 20 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

NLnet Labs Unbound 1.16.2 up to and including version 1.25.0 has a vulnerability of the 'ghost domain names' family of attacks that could extend the ghost domain window by up to one cached TTL configured value. Similar to other 'ghost domain names' attacks, an adversary needs to control a (ghost) zone and be able to query a vulnerable Unbound. A single client NS query can cause Unbound to overwrite the cached expired parent-side referral NS rrset with the child-side apex NS rrset and essentially extend the ghost domain window by up to one cached TTL configured value ('cache-max-ttl'). In configurations where 'harden-referral-path: yes' is used (non-default configuration), no client NS query is required since Unbound implicitly performs that query. Unbound 1.25.1 contains a patch with a fix that does not allow extension of TTLs for (parent) NS records regardless of their trust.

Weakness: CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2026-40622?

It affects 1 product.


Products: Nlnetlabs Unbound.

## How do I fix CVE-2026-40622?

Upgrade to a fixed version.

## Is CVE-2026-40622 being exploited?

There is no known exploitation of CVE-2026-40622 in the wild and no public exploit code.

## Other vulnerabilities in Nlnetlabs Unbound

- [CVE-2026-81642](https://insights.sbomify.com/CVE-2026-81642/): Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY (critical 9.1)
- [CVE-2026-33278](https://insights.sbomify.com/CVE-2026-33278/): Possible arbitrary code execution during DNSSEC validation (critical 9.1)
- [CVE-2026-42944](https://insights.sbomify.com/CVE-2026-42944/): Heap overflow with multiple NSID, COOKIE, PADDING EDNS options (high 8.7)
- [CVE-2026-42959](https://insights.sbomify.com/CVE-2026-42959/): Crash during DNSSEC validation of malicious content (high 8.7)
- [CVE-2026-82717](https://insights.sbomify.com/CVE-2026-82717/): CNAME synthesis could lead to heap corruption (high 8.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40622 and fix it if it is affected.

What it is: CVE-2026-40622 is a medium-severity vulnerability in Nlnetlabs Unbound, published on 20 May 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-2026-40622 in the wild and no public exploit code.

Affected product: Nlnetlabs Unbound. 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-2026-40622/ (Markdown: https://insights.sbomify.com/CVE-2026-40622/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40622
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40622
- OSV: https://osv.dev/vulnerability/CVE-2026-40622

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40622/
Summaries are generated and may contain mistakes; the official description above is the record.