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CVE-2020-12667

Knot Resolver before 5.1.1 allows traffic amplification via a crafted DNS answer from an attacker...

7.5 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

2.61%Up 1.4 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used 7.5

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.

Record
CVE-2020-12667
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness
CWE-400
Updated
2026-11-02
CVE List 7.5

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.

Record
CVE-2020-12667
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-02
EUVDEUVD-2020-4965 7.5

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.

Record
EUVD-2020-4965
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-03
GitHub AdvisoriesGHSA-2gpj-6wgq-8636 7.5

Knot Resolver before 5.1.1 allows traffic amplification via a crafted DNS answer from an attacker...

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.

Record
GHSA-2gpj-6wgq-8636
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-02
OSVALPINE-CVE-2020-12667 7.5

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.

Record
ALPINE-CVE-2020-12667
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-03
OSV 7.5

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.

Record
CVE-2020-12667
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2020-12667 7.5

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.

Record
DEBIAN-CVE-2020-12667
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2020-12667 7.5

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.

Record
UBUNTU-CVE-2020-12667
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVUSN-7047-1 No score

knot-resolver vulnerabilities

Vladimír Čunát discovered that Knot Resolver incorrectly handled input during DNSSEC validation. A remote attacker could possibly use this issue to bypass certain validations. (CVE-2019-10190)

Vladimír Čunát discovered that Knot Resolver incorrectly handled input during DNSSEC validation. A remote attacker could possibly use this issue to downgrade DNSSEC-secure domains to a DNSSEC-insecure state, resulting in a domain hijacking attack. (CVE-2019-10191)

Vladimír Čunát discovered that Knot Resolver incorrectly handled certain DNS replies with many resource records. An attacker could possibly use this issue to consume system resources, resulting in a denial of service. (CVE-2019-19331)

Lior Shafir, Yehuda Afek, and Anat Bremler-Barr discovered that Knot Resolver incorrectly handled certain queries. A remote attacker could use this issue to perform an amplification attack directed at a target. (CVE-2020-12667)

Record
USN-7047-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
knot-resolver
Alpine:v3.11
before 4.3.0-r3
4.3.0-r3
knot-resolver
Alpine:v3.12
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.13
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.14
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.15
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.16
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.17
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.18
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.19
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.20
before 5.1.1-r0
5.1.1-r0
Show 11 moreShow less
Affected packages
PackageAffectedFixed
knot-resolver
Alpine:v3.21
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.22
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.23
before 5.1.1-r0
5.1.1-r0
knot-resolver
Alpine:v3.24
before 5.1.1-r0
5.1.1-r0
knot-resolver
Debian:12
before 5.1.1-0.1
5.1.1-0.1
knot-resolver
Debian:13
before 5.1.1-0.1
5.1.1-0.1
knot-resolver
Debian:14
before 5.1.1-0.1
5.1.1-0.1
knot-resolver
Debian:10
before 3.2.1-3+deb10u2, plus listed versions
3.2.1-33.2.1-3+deb10u1
3.2.1-3+deb10u2
knot-resolver
Ubuntu:Pro:16.04:LTS
All versions, plus listed versions
1.0.0~beta2-123-g6134920-11.0.0~beta3-11.0.0~beta3-1ubuntu0.1~esm1
None known
knot-resolver
Ubuntu:Pro:18.04:LTS
All versions, plus listed versions
1.3.3-11.5.0-41.5.1-11.5.2-12.0.0-3
Show 4 moreShow less
2.1.0-12.1.0-22.1.1-12.1.1-1ubuntu0.1~esm2
None known
knot-resolver
Ubuntu:20.04:LTS
before 3.2.1-3ubuntu2.2, plus listed versions
3.2.1-33.2.1-3ubuntu13.2.1-3ubuntu23.2.1-3ubuntu2.1
3.2.1-3ubuntu2.2

History

History
RecordedChangedSources
affected, aliases, referencesOSV
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2020-12667 is a high vulnerability (CVSS 7.5) in Nic Knot Resolver, published May 19, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 2.61%, the 85th percentile. Fixed in knot-resolver 4.3.0-r3.

References

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