Knot Resolver before 5.1.1 allows traffic amplification via a crafted DNS answer from an…
Priority MEDIUM 44CWE-400Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- No fix listed
Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA. Impact type from CWE-400.
Summary
Knot Resolver before 5.1.1 allows traffic amplification via a crafted DNS answer from an attacker-controlled server, aka an "NXNSAttack" issue. This is triggered by random subdomains in the NSDNAME in NS records.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.02612 85th percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | — | all versions | — | No fix listed | CNA |
- — Vendor— Affected all versions Fixed in — No fix listed CNA
Remediation
No fixed version listed by the sources yet.
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2020-12667
- 2026-10-03 Alias added: GHSA-2gpj-6wgq-8636
References
Advisory 5
- https://en.blog.nic.cz/2020/05/19/nxnsattack-upgrade-resolvers-to-stop-new-kind-of-random-subdomain-attack/
- https://www.knot-resolver.cz/2020-05-19-knot-resolver-5.1.1.html
- [oss-security] 20200519 [CVE-2020-12667] Knot Resolver 5.1.1 NXNSAttack mitigation
- http://cyber-security-group.cs.tau.ac.il/#
- FEDORA-2020-bf68101ad3
More CZ.NIC Knot Resolver vulnerabilities
- TI-2023-27571 Certain DNSSEC aspects of the DNS protocol (in RFC 4033, 4034, 4035, 6840, and related… CVSS 3.1HIGH 7.5
- TI-2022-19055 Knot Resolver before 5.5.3 allows remote attackers to cause a denial of service (CPU… CVSS 3.1HIGH 7.5
- TI-2023-24930 Knot Resolver before 5.7.0 performs many TCP reconnections upon receiving certain nonsensical responses from servers. CVSS 3.1HIGH 7.5
- TI-2023-11416 Knot Resolver before 5.6.0 enables attackers to consume its resources, launching… CVSS 3.1HIGH 7.5
- TI-2019-13943 knot-resolver before version 4.3.0 is vulnerable to denial of service through high CPU… CVSS 3.1HIGH 7.5
- TI-2019-07512 Improper input validation in CZ.NIC knot-resolver CVSS 3.1HIGH 7.5
Sources
- CVE-2020-12667 · CVE Program
- CVE-2020-12667 · NVD
- FIRST EPSS
- GHSA-2gpj-6wgq-8636 · GitHub Advisory Database · CC BY 4.0
- CVE-2020-12667 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences