Description
Any remote client can crash a (debugging/non-release build type) NSD serve child by sending it a special crafted message with a specially tuned number of DNS Cookie options (17 when UDP payload size is 512). By continuously crashing the serve childs, the remote client can severely hamper or, when positioned sufficiently close, deny all DNS service.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| NLnet Labs | NSD | 4.3.7 – < 4.15.1 | 4.15.1 |
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 | nsd | 4.15.1-1 | — |
| Debian 13 | nsd | No fix yet | — |
| Debian 12 | nsd | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | nsd | No fix yet | — |
Show 6 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 26.04 LTS | nsd | No fix yet | — |
| Ubuntu Pro 24.04 LTS | nsd | No fix yet | — |
| Ubuntu Pro 22.04 LTS | nsd | No fix yet | — |
| Ubuntu Pro 20.04 LTS | nsd | No fix yet | — |
| Ubuntu Pro 18.04 LTS | nsd | No fix yet | — |
| Ubuntu Pro 16.04 LTS | nsd | No fix yet | — |
Advisories 1
- WID-SEC-2026-3663 OpenBSD: Mehrere Schwachstellen BSI CERT-Bund (WID) · Sep 29, 2026
References
- https://www.nlnetlabs.nl/downloads/nsd/CVE-2026-19401.txt vendor-advisory