What’s Vulnerable › Vulnerabilities

CVE-2020-12667

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-05-19 · updated 2026-06-17
• Weakness: CWE-400

Description

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.

Affected products

• CZ.NIC knot-resolver: before 5.1.1 — fixed in 5.1.1

How to fix

Upgrade to a fixed version: CZ.NIC knot-resolver 5.1.1. Check the vendor advisory for mitigations.

References

• http://cyber-security-group.cs.tau.ac.il/#
• http://www.openwall.com/lists/oss-security/2020/05/19/2
• https://en.blog.nic.cz/2020/05/19/nxnsattack-upgrade-resolvers-to-stop-new-kind-of-random-subdomain-attack/
• https://lists.debian.org/debian-lts-announce/2024/04/msg00017.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/76Y4FITMOH6RVPWAANGV7NB2ZHPJJGDQ/
• https://www.knot-resolver.cz/2020-05-19-knot-resolver-5.1.1.html
• http://cyber-security-group.cs.tau.ac.il/#
• http://www.openwall.com/lists/oss-security/2020/05/19/2
• https://en.blog.nic.cz/2020/05/19/nxnsattack-upgrade-resolvers-to-stop-new-kind-of-random-subdomain-attack/
• https://lists.debian.org/debian-lts-announce/2024/04/msg00017.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/76Y4FITMOH6RVPWAANGV7NB2ZHPJJGDQ/
• https://www.knot-resolver.cz/2020-05-19-knot-resolver-5.1.1.html

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