Description
knot-resolver before version 4.3.0 is vulnerable to denial of service through high CPU utilization. DNS replies with very many resource records might be processed very inefficiently, in extreme cases taking even several CPU seconds for each such uncached message. For example, a few thousand A records can be squashed into one DNS message (limit is 64kB).
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| CZ.NIC | knot-resolver | 4.3.0 | — |
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 | 5.0.1-1 | — |
| Debian 13 | knot-resolver | 5.0.1-1 | — |
| Debian 12 | knot-resolver | 5.0.1-1 | — |
| 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 | 4.3.0-r0 | — |
| Alpine v3.23 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.22 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.21 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.20 | knot-resolver | 4.3.0-r0 | — |
Show 9 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.18 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.17 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.16 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.15 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.14 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.13 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.12 | knot-resolver | 4.3.0-r0 | — |
| Alpine v3.11 | knot-resolver | 4.3.0-r0 | — |
Advisories 2
- 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