CVE-2026-12244 Heap overflow and crash with crafted SVCB RR
A secondary NSD server can be crashed or subjected to remote code execution by a malicious primary zone via a crafted SVCB record causing an integer overflow.
- 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-2026-12244?
CVE-2026-12244 is a high-severity vulnerability in NLnet Labs NSD, published on 25 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
If NSD is configured as secondary for a zone, the primary of that zone can crash NSD with an AXFR containing a DNS message with a special crafted SVCB RR with an rdata size of 65512, that let's an (uint16_t) variable that is used to allocate space needed for the RR wrap (because total size > 65535), causing a heap overflow. The attacker can perform a controlled (RCE class) head write of up to 65509 bytes
Which versions are affected by CVE-2026-12244?
It affects 1 product.
Products include Nlnetlabs Nsd.
How do I fix CVE-2026-12244?
Apply the vendor's patch.
Is CVE-2026-12244 being exploited?
There is no known exploitation of CVE-2026-12244 in the wild and no public exploit code.
Other vulnerabilities in NLnet Labs NSD
- 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
- CVE-2026-12490 Bypass of client certificate verification with transfer over TLS
Sources
Also known as ALPINE-CVE-2026-12244, DEBIAN-CVE-2026-12244, GHSA-p22w-wq6p-g85g.