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Vulnerability record · CVE-2021-40083 · published 25 August 2021

CVE-2021-40083: Nic knot resolver vulnerability

Nic · Knot Resolver

Knot 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 for a positive wildcard proof).

7.5 CVSS 3.1 High EPSS 1.4% · top 28.1% CWE-617 · CWE-617
7.5CVSS 3.1 base score, v2 5.0
1.4%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
17 Jun 2026Last modified by NVD

Description

Knot 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 for a positive wildcard proof).

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
https://gitlab.nic.cz/knot/knot-resolver/-/merge_requests/1169 PatchThird Party Advisory
https://gitlab.nic.cz/knot/knot-resolver/-/merge_requests/1169 PatchThird Party 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-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-2020-12667Nic knot resolver uncontrolled resource consumption vulnerabilityKnot Resolver before 5.1.1 allows traffic amplification via a crafted DNS answer from an attacker-controlled server, aka an "NXNSAttack" issue. This …EPSS 2.5%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-2019-10190Nic knot resolver improper input validation vulnerabilityA vulnerability was discovered in DNS resolver component of knot resolver through version 3.2.0 before 4.1.0 which allows remote attackers to bypass …EPSS 2.0%

Source: NIST National Vulnerability Database (record CVE-2021-40083), CISA KEV, FIRST EPSS (scores of 2026-10-02). This page is refreshed as NVD updates the record.