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Vulnerability record · CVE-2020-12667 · published 19 May 2020

CVE-2020-12667: Nic knot resolver uncontrolled resource consumption vulnerability

Nic · Knot Resolver

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.

7.5 CVSS 3.1 High EPSS 2.5% · top 15.5% CWE-400 · Uncontrolled resource consumption
7.5CVSS 3.1 base score, v2 5.0
2.5%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
12References
17 Jun 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://cyber-security-group.cs.tau.ac.il/# Technical DescriptionThird Party Advisory
http://www.openwall.com/lists/oss-security/2020/05/19/2 Mailing ListThird Party Advisory
https://en.blog.nic.cz/2020/05/19/nxnsattack-upgrade-resolvers-to-stop-new-kind-of-random-subdomain-attack/ Technical DescriptionVendor Advisory
https://lists.debian.org/debian-lts-announce/2024/04/msg00017.html
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/76Y4FITMOH6RVPWAANGV7NB
https://www.knot-resolver.cz/2020-05-19-knot-resolver-5.1.1.html Release NotesVendor Advisory
http://cyber-security-group.cs.tau.ac.il/# Technical DescriptionThird Party Advisory
http://www.openwall.com/lists/oss-security/2020/05/19/2 Mailing ListThird Party Advisory
https://en.blog.nic.cz/2020/05/19/nxnsattack-upgrade-resolvers-to-stop-new-kind-of-random-subdomain-attack/ Technical DescriptionVendor Advisory
https://lists.debian.org/debian-lts-announce/2024/04/msg00017.html
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/76Y4FITMOH6RVPWAANGV7NB
https://www.knot-resolver.cz/2020-05-19-knot-resolver-5.1.1.html Release NotesVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

7.5CVE-2023-50387DNSSEC KeyTrap flaw in DNS resolvers causes CPU exhaustion DoSCVE-2023-50387, known as KeyTrap, is a flaw in DNSSEC validation logic where a zone containing many DNSKEY and RRSIG records forces resolvers to eval…EPSS 100%analysed7.5CVE-2023-46317Nic knot resolver vulnerabilityKnot Resolver before 5.7.0 performs many TCP reconnections upon receiving certain nonsensical responses from servers.EPSS 0.64%7.5CVE-2023-26249Nic knot resolver allocation without limits vulnerabilityKnot Resolver before 5.6.0 enables attackers to consume its resources, launching amplification attacks and potentially causing a denial of service. S…EPSS 0.71%7.5CVE-2022-40188Nic knot resolver vulnerabilityKnot Resolver before 5.5.3 allows remote attackers to cause a denial of service (CPU consumption) because of algorithmic complexity. During an attack…EPSS 1.9%7.5CVE-2021-40083Nic knot resolver vulnerabilityKnot Resolver before 5.3.2 is prone to an assertion failure, triggerable by a remote attacker in an edge case (NSEC3 with too many iterations used fo…EPSS 1.4%7.5CVE-2018-1110Nic knot resolver improper input validation vulnerabilityA flaw was found in knot-resolver before version 2.3.0. Malformed DNS messages may cause denial of service.EPSS 1.1%7.5CVE-2019-19331Nic knot resolver improper resource shutdown vulnerabilityknot-resolver before version 4.3.0 is vulnerable to denial of service through high CPU utilization. DNS replies with very many resource records might…EPSS 2.2%7.5CVE-2019-10191Nic knot resolver improper input validation vulnerabilityA vulnerability was discovered in DNS resolver of knot resolver before version 4.1.0 which allows remote attackers to downgrade DNSSEC-secure domains…EPSS 1.9%

Source: NIST National Vulnerability Database (record CVE-2020-12667), CISA KEV, FIRST EPSS (scores of 2026-10-01). This page is refreshed as NVD updates the record.