Nlnetlabs Nsd vulnerabilities

CVE-2026-101341 High · 8.7 CWE-121 Oct 14, 2026

Stack overwrite from specially formatted TXT-DATA RDATA field

Tokens of text in RDATA (of for example TXT records) under 32 bytes are not checked to stay within the space reserved for the RDATA allowing for arbitrary sized out of bound stack writes, including an overwrite of a callback function pointer which is called directly after parse. Zone files which are written out by NSD itself, such for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).

CVE-2026-101339 High · 8.7 CWE-121 Oct 14, 2026

Stack overwrite from a specially crafted and formatted HIP RR

A HIP resource record that fills the RDATA near or at is limit, and has another dname RDATA field (a HIP Rendezvous server) can overwrite the stack with up to 191 bytes of attacker controlled data. Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).

CVE-2026-101338 High · 8.7 CWE-121 Oct 14, 2026

Stack overwrite from a specially crafted and formatted SVCB or HTTPS RR

When a SVCB or HTTPS RR has filled the wire format RDATA up to the brim, another ECH parameter may overwrite the stack, and once beyond the limit, the base64 decoder can write attacker controlled data of unlimited size. Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).

CVE-2026-101337 High · 8.7 CWE-121 Oct 14, 2026

Stack overwrite from specially formatted base64 RDATA field

When base64 data is split up in pieces, of 3 character or less, tokens were incorrectly calculated to produce 0 bytes. This enables attackers to overwrite the stack with up to 64K of attacker controlled data. Zone files which are written out by NSD itself, such as for zones for which the NSD instance is secondary, will not be formatted like this. The zone file must be fed to NSD directly, (but it could come, for example, from an operator controlled provisioning system).

CVE-2026-19538 High · 7.5 CWE-290 Aug 26, 2026

Bypass of BLOCKED ACL items on proxy protocol port over TCP or TLS

The BLOCKED access control list items that are evaluated to deny access on the the proxy protocol port can be bypassed completely when connecting over TCP or TLS and sending the query twice on connection that is kept open.

CVE-2026-19401 High · 7.5 CWE-400 Aug 26, 2026

Remote UDP DoS by sending multiple DNS Cookie options

Any remote client can crash a (debugging/non-release build type) NSD serve child by sending it a special crafted message with a specially tuned number of DNS Cookie options (17 when UDP payload size is 512). By continuously crashing the serve childs, the remote client can severely hamper or, when positioned sufficiently close, deny all DNS service.

CVE-2026-18916 High · 7.5 CWE-191 Aug 26, 2026

Remote TCP DoS by throttling the TCP receive window

Any remote client can crash a NSD serve child, by throttling the TCP receive window after a TCP query. By continuously crashing the serve childs, the remote client can denial all TCP service to this NSD instance.

CVE-2026-18664 Critical · 9.1 CWE-284 Aug 26, 2026

Wrong interpretation of ACL ranges

When ranges are used for access control (i.e. of the form 1.2.3.4-1.2.3.25), because NSD wrongly compares the IP address with the range on little endian systems, IPs that were meant to be allowed may be denied, and, IPs that were meant to be denied access could be allowed. An IPv4 address is compared with IPv4 ranges as unsigned 32 bit numbers directly with the endianness of the host, but the values to compare are in network byte order (big-endian). With IPv6 addresses the comparison is done in 4 times a unsigned 32 bit number comparison, again with the endianness of the host where all values are actually in network bye order.

CVE-2026-12490 High · 7.5 CWE-284 Jun 25, 2026

Bypass of client certificate verification with transfer over TLS

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.

CVE-2026-12246 High · 8.1 CWE-20 Jun 25, 2026

Out of bounds stack write with crafted APL RR

NSD version 4.14.0 introduced a bug where a specially crafted APL RR, with an adflength larger than permitted for the address family will overwrite the stack when the zone is written to disk, with a maximum of 111 attacker controlled bytes.

CVE-2026-12245 High · 7.5 CWE-416 Jun 25, 2026

Denial of DNS over TLS service by any DoT client

NSD from version 4.13.0 has a heap use-after-free bug in logging errors on TLS connections, causing a crash of the server process, which can be triggered trivially by sending a DNS query over a DoT connection, and closing the connection without reading the response.

CVE-2026-12244 High · 8.8 CWE-122 Jun 25, 2026

Heap overflow and crash with crafted SVCB RR

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