CVE-2026-12490 Bypass of client certificate verification with transfer over TLS
Attackers can bypass client certificate verification for DNS zone transfers by using the standard TLS or TCP port instead of the dedicated authentication port.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-12490?
CVE-2026-12490 is a high-severity authentication bypass vulnerability in NLnet Labs NSD, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
When a provide-xfr is given with a tls-auth-name, a secondary requesting a transfer should provide a client certificate with that name. However, no client certificate is needed when the request comes in over TLS over the regular tls-port (and not the tls-auth-port) or over over TCP over the regular port, when the other conditions of the provide-xfr rule match.
Which versions are affected by CVE-2026-12490?
It affects 1 product.
Products include Nlnetlabs Nsd.
How do I fix CVE-2026-12490?
Apply the vendor's patch.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-12490 being exploited?
There is no known exploitation of CVE-2026-12490 in the wild and no public exploit code.
Other vulnerabilities in NLnet Labs NSD
- CVE-2026-12244 Heap overflow and crash with crafted SVCB RR
- CVE-2026-12245 Denial of DNS over TLS service by any DoT client
- CVE-2026-18664 Wrong interpretation of ACL ranges
- CVE-2026-19401 Remote UDP DoS by sending multiple DNS Cookie options
- CVE-2026-19538 Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS
Sources
Also known as ALPINE-CVE-2026-12490, DEBIAN-CVE-2026-12490, GHSA-27xx-c7vg-hjjj, UBUNTU-CVE-2026-12490, USN-8474-1.