CVE-2026-39155 Denial of service in n/a
Attackers can cause downstream resolver denial of service by exploiting incorrect NSEC owner name computation in Knot DNS online signing.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-39155?
CVE-2026-39155 is a medium-severity denial of service vulnerability in n/a, published on 23 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Knot DNS before 3.4.10 and 3.5.x before 3.5.4 contains a vulnerability in mod-onlinesign where the next NSEC owner name can be computed incorrectly. This can create an overly broad authenticated denial interval, allowing downstream validating resolvers using aggressive negative caching to synthesize negative answers for legitimate names and causing resolver-side denial of service.
Weakness: CWE-345
Which versions are affected by CVE-2026-39155?
How do I fix CVE-2026-39155?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-39155 being exploited?
There is no known exploitation of CVE-2026-39155 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-39155, GHSA-hxf3-75wr-4mhp, UBUNTU-CVE-2026-39155.