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.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | knot-resolver | 5.1.1-0.1 | — |
| Debian 13 | knot-resolver | 5.1.1-0.1 | — |
| Debian 12 | knot-resolver | 5.1.1-0.1 | — |
| Debian 10 | knot-resolver | 3.2.1-3+deb10u2 | DLA-3795-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | knot-resolver | 3.2.1-3ubuntu2.2 | USN-7047-1 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 18.04 LTS | knot-resolver | No fix yet | — |
| Ubuntu Pro 16.04 LTS | knot-resolver | No fix yet | — |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.23 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.22 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.21 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.20 | knot-resolver | 5.1.1-r0 | — |
Show 9 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.18 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.17 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.16 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.15 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.14 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.13 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.12 | knot-resolver | 5.1.1-r0 | — |
| Alpine v3.11 | knot-resolver | 4.3.0-r3 | — |
Advisories 3
- USN-7047-1 knot-resolver vulnerabilities Ubuntu Security Notices (USN) · Apr 27, 2026
- DLA-3795-1 knot-resolver - security update Debian Security (DSA / DLA) · Mar 9, 2026
- WID-SEC-2024-0978 Mehrere DNS Server: Schwachstelle ermöglicht Denial of Service BSI CERT-Bund (WID) · Oct 1, 2024
References
- 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 mailing-list
- http://cyber-security-group.cs.tau.ac.il/#
- FEDORA-2020-bf68101ad3 vendor-advisory
- [debian-lts-announce] 20240426 [SECURITY] [DLA 3795-1] knot-resolver security update mailing-list