Vulnerability · Published May 20, 2026 · Assigned by NLnet Labs
CVE-2026-40622Another 'ghost domain names' attack variant
Medium 6.6
In plain English
A medium-severity security flaw in Unbound from NLnet Labs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 4% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
NLnet Labs Unbound 1.16.2 up to and including version 1.25.0 has a vulnerability of the 'ghost domain names' family of attacks that could extend the ghost domain window by up to one cached TTL configured value. Similar to other 'ghost domain names' attacks, an adversary needs to control a (ghost) zone and be able to query a vulnerable Unbound. A single client NS query can cause Unbound to overwrite the cached expired parent-side referral NS rrset with the child-side apex NS rrset and essentially extend the ghost domain window by up to one cached TTL configured value ('cache-max-ttl'). In configurations where 'harden-referral-path: yes' is used (non-default configuration), no client NS query is required since Unbound implicitly performs that query. Unbound 1.25.1 contains a patch with a fix that does not allow extension of TTLs for (parent) NS records regardless of their trust.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | python3-unbound | 1.24.2-7.el10_2.2 | ALSA-2026:36320 |
| AlmaLinux:8 | python3-unbound | 1.16.2-5.12.el8_10 | ALSA-2026:37282 |
| AlmaLinux:9 | python3-unbound | 1.24.2-3.el9_8.2 | ALSA-2026:36777 |
| AlmaLinux:10 | unbound | 1.24.2-7.el10_2.2 | ALSA-2026:36320 |
| AlmaLinux:8 | unbound | 1.16.2-5.12.el8_10 | ALSA-2026:37282 |
| AlmaLinux:9 | unbound | 1.24.2-3.el9_8.2 | ALSA-2026:36777 |
| AlmaLinux:10 | unbound-anchor | 1.24.2-7.el10_2.2 | ALSA-2026:36320 |
| AlmaLinux:10 | unbound-devel | 1.24.2-7.el10_2.2 | ALSA-2026:36320 |
| AlmaLinux:8 | unbound-devel | 1.16.2-5.12.el8_10 | ALSA-2026:37282 |
| AlmaLinux:9 | unbound-devel | 1.24.2-3.el9_8.2 | ALSA-2026:36777 |
| AlmaLinux:10 | unbound-dracut | 1.24.2-7.el10_2.2 | ALSA-2026:36320 |
| AlmaLinux:9 | unbound-dracut | 1.24.2-3.el9_8.2 | ALSA-2026:36777 |
| AlmaLinux:10 | unbound-libs | 1.24.2-7.el10_2.2 | ALSA-2026:36320 |
| AlmaLinux:8 | unbound-libs | 1.16.2-5.12.el8_10 | ALSA-2026:37282 |
| AlmaLinux:9 | unbound-libs | 1.24.2-3.el9_8.2 | ALSA-2026:36777 |
| AlmaLinux:10 | unbound-utils | 1.24.2-7.el10_2.2 | ALSA-2026:36320 |
| Alpine:v3.22 | unbound | 1.25.2-r0 | ALPINE-CVE-2026-40622 |
| Alpine:v3.23 | unbound | 1.25.2-r0 | ALPINE-CVE-2026-40622 |
| Alpine:v3.24 | unbound | 1.25.1-r0 | ALPINE-CVE-2026-40622 |
| Debian:12 | unbound | no fix listed | DEBIAN-CVE-2026-40622 |
| Debian:13 | unbound | 1.26.1-0+deb13u1 | DEBIAN-CVE-2026-40622 |
| Debian:14 | unbound | 1.25.2-1 | DEBIAN-CVE-2026-40622 |
| Rocky Linux:10 | unbound | 0:1.24.2-7.el10_2.2 | RLSA-2026:36320 |
| Rocky Linux:8 | unbound | 0:1.16.2-5.12.el8_10 | RLSA-2026:37282 |
| Rocky Linux:9 | unbound | 0:1.24.2-3.el9_8.2 | RLSA-2026:36777 |
| Ubuntu:24.04:LTS | unbound | 1.19.2-1ubuntu3.8 | UBUNTU-CVE-2026-40622 |
| Ubuntu:25.10 | unbound | 1.22.0-2ubuntu2.3 | UBUNTU-CVE-2026-40622 |
| Ubuntu:26.04:LTS | unbound | 1.24.2-1ubuntu2.1 | UBUNTU-CVE-2026-40622 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| NLnet Labs | Unbound | 1.16.2 – before 1.25.1 |
Weakness: CWE-346 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:U/U:Amber
References
- https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40622.txt vendor-advisory