What’s Vulnerable › Vulnerabilities
CVE-2026-40622: Another 'ghost domain names' attack variant
- Severity: high (CVSS 7.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.1% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-05-20 · updated 2026-07-24
- Weakness: CWE-346
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 products
- NLnet Labs Unbound: from 1.16.2 before 1.25.1 — fixed in 1.25.1
How to fix
Upgrade to a fixed version: NLnet Labs Unbound 1.25.1. Check the vendor advisory for mitigations.
References
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