HIGH CVSS 7.5
Published: 2026-05-20

CVE-2026-40622

nlnetlabs unbound Security Advisory (CVE-2026-40622)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-40622 impacting nlnetlabs unbound. Evaluated with CVSS Base Score of 7.5 (HIGH).

Original NVD Description

Source: NIST NVD
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.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Network (AV:N)
Exploitable remotely across internet boundaries
Attack Complexity
Low (AC:L)
No specialized conditions required
Privileges Required
None (PR:N)
Unauthenticated execution
User Interaction
None (UI:N)
Zero human interaction required
Scope
Unchanged (S:U)
Confined to same security context
Confidentiality
None (C:N)
No data confidentiality impact
Integrity
High (I:H)
Total modification of target system
Availability
None (A:N)
No system availability impact

🎯 Affected Versions Matrix

Affected Product nlnetlabs / unbound
Affected Versions *
Weakness Enumeration CWE-346

Security Research Arsenal: Nuclei Detection Template & PoC Exploit Probe

High-Intent Research Tool

Ready-to-use security scanner signatures, active verification probe skeletons, and remediation playbooks for CVE-2026-40622 impacting nlnetlabs unbound.

⚡ Nuclei Detection Template (YAML) cve-2026-40622.yaml
id: cve-2026-40622

info:
  name: nlnetlabs unbound - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: high
  description: |
    Automated signature & scanner for CVE-2026-40622 affecting nlnetlabs unbound.
    Evaluation: 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 ex...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-40622
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
    cvss-score: 7.5
    cve-id: CVE-2026-40622
    cwe-id: CWE-346
  tags: cve,cve-2026-40622,nlnetlabs,unbound,high

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "unbound"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2026-40622.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-40622
# Target: nlnetlabs unbound | CVSS: 7.5 (HIGH)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-40622 (nlnetlabs unbound)...")
    headers = {
        "User-Agent": "CyberVault-Audit-Scanner/2.0",
        "Accept": "*/*"
    }
    try:
        r = requests.get(f"{target_url.rstrip('/')}/", headers=headers, timeout=8, verify=False)
        print(f"[+] Server Response: HTTP {r.status_code} | Server Banner: {r.headers.get('Server', 'Unknown')}")
        if r.status_code < 500:
            print(f"[!] Target reachable. Verify version against nlnetlabs unbound scope (*).")
        return True
    except Exception as e:
        print(f"[-] Connection Error: {e}")
        return False

if __name__ == '__main__':
    url = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:8080"
    verify_vulnerability(url)
🛡️ Quick Patch & Remediation Script (Bash) patch_cve-2026-40622.sh
# Recommended Remediation & Patching Commands for CVE-2026-40622
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install unbound 2>/dev/null || \
sudo dnf upgrade unbound 2>/dev/null || \
sudo yum update unbound

# 2. Inspect installed package versions for vulnerable scope:
dpkg -l | grep -i unbound 2>/dev/null || rpm -qa | grep -i unbound

# 3. Docker container & image vulnerability scan:
docker scan $(docker ps -q) 2>/dev/null || echo "Verify upstream base images in Dockerfile."

🛡️ Remediation & Security Action

  • Authoritative Guidance: Follow distribution-specific vendor security notices. Advisory status and package patches vary by distribution release.
  • Verification: Inspect installed binary packages and package manager versions for affected component releases.
  • Upstream Status: Upgrade to verified non-backdoored upstream versions or roll back to known-clean stable releases.
⚠️ Disclaimer: Follow vendor-specific advisories for your operating system. CyberVault does not fabricate unsupported remediation scripts.

🔗 Verified Technical References

Authorities
  • No records filed in this category.
Distributions
  • No records filed in this category.

❓ Frequently Asked Questions (FAQ) & Remediation Guide

How do I fix CVE-2026-40622 in nlnetlabs unbound?

Review vendor-specific security notices and update nlnetlabs unbound packages to the latest patched release immediately. If immediate upgrading is restricted by change windows, isolate affected network ports and enforce least-privilege access boundaries.

Is there an active exploit or public PoC for CVE-2026-40622?

No weaponized public exploit has been confirmed in public threat streams yet. Continuous surveillance is active across GitHub and security feeds.

What is the CVSS 3.1 severity rating and impact for CVE-2026-40622?

CVE-2026-40622 is classified with a CVSS 3.1 Base Score of 7.5 (HIGH). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
7.5
HIGH SEVERITY
CVE ID CVE-2026-40622
Weakness CWE-346
Vendor nlnetlabs
Product unbound
Published 2026-05-20
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N