Last updated 22 May 2026

Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY

A multi-vendor cache poisoning vulnerability named 'Rebirthday Attack' has been discovered in caching resolvers that support EDNS Client Subnet (ECS). Unbound is also vulnerable when compiled with ECS support, i.e., '--enable-subnet', AND configured to send ECS information along with queries to upstream name servers, i.e., at least one of the 'send-client-subnet', 'client-subnet-zone' or 'client-subnet-always-forward' options is used. Resolvers supporting ECS need to segregate outgoing queries to accommodate for different outgoing ECS information. This re-opens up resolvers to a birthday paradox attack (Rebirthday Attack) that tries to match the DNS transaction ID in order to cache non-ECS poisonous replies.

A vulnerability was found in Unbound that results in heap overflow when encoding multiple NSID and/or DNS Cookie EDNS and/or EDNS Padding options in the reply packet. The relevant options ('nsid', 'answer-cookie', 'pad-responses' (default)) need to be enabled for the vulnerability to be exploited.

Unbound 1.25.1 includes a fix to de-duplicate the EDNS options and a fix to prevent truncation of the EDNS field size calculation that also contributes to the heap overflow.

Access of Uninitialized Pointer vulnerability in the DNSSEC validator of the Unbound DNS resolver. The flaw is caused by the use of incorrect counters when calculating write offsets for ADDITIONAL section rrsets in chase-reply messages. DNAME duplication can increase the ANSWER section count and authority filtering can decrease the AUTHORITY section count, creating an uninitialized array slot. The validator later dereferences this uninitialized pointer, causing an immediate process crash. An adversary controlling a DNSSEC-signed domain can trigger this bug with a single query by configuring a DNAME chain with unsigned CNAMEs and a response containing unsigned AUTHORITY records alongside signed ADDITIONAL glue records.

When Routinator encounters a file via RRDP using a specifically crafted Document Type Definition, Routinator crashes.

Routinator exits on any error when accepting incoming HTTP or RTR connections, including ones it can recover from such as running out of file descriptors. This condition can be triggered maliciously by an attacker by opening a large number of connections to the HTTP or RTR server.

This only affects users that make their HTTP or RTR server available to untrusted networks.

Last updated 29 June 2026

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).

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).

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).

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).

CNAME synthesis could lead to heap corruption

When a CA's parent lives on the same Krill server: instead of building and verifying a signed CMS message, it runs the RFC 6492 provisioning exchange in-process and trusts the child identity (childhandle) that the caller put in the parent contact. Nothing checks that this child identity actually belongs to the CA making the request.

The vulnerability is that Krill encrypts every login-session token with a nonce built from a counter that is reset to 0 on every Krill restart, so the same (key, nonce) pair is used again after each restart.

Routinator does not properly check the module component of rsync URIs, which are used to create the file system paths for the Routinator cache. This allows for path traversal by having a module name containing .., potentially providing an attacker access to the entire Routinator rsync cache.

When sending a specifically crafted non-UTF-8 string as select-asn query parameter to the /api/v1/origins endpoint, Routinator crashes.

This only affects users who allow API access from untrusted networks.

Insufficient verification that responses belong to a query

When Routinator encounters an RRDP notification file with gaps in the delta entries, it is still accepted and parsed, potentially leading to missing data. If it encounters too many delta entries it may run out of memory.

Due to a mistake in error checking, Routinator will terminate when an incoming RTR connection is reset by the peer too quickly after opening.

The initial code parsing the manifest did not check the content of the file names yet later code assumed that it was checked and panicked when encountering illegal characters, resulting in a crash of Routinator.

Cross-zone wildcard cache poisoning via RRSIG.labels manipulation

In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, when downstream DNS-over-QUIC (DoQ) is enabled, the first two bidirectional streams on a new QUIC connection (streamid 0 and 4) bypass the per-stream 'quic-size' gate entirely, and large input buffers are allocated later, after only the 2-byte length prefix has been received from the initial streams. As a result, a remote client can make Unbound exceed the configured 'quic-size' limit with low-cost input. Using only one connection and two streams, each sending a declared 65535-byte length prefix and then holding the streams open, a client can already trivially make Unbound roughly allocate double that amount. This is a remote availability issue / memory-accounting bypass in the downstream DoQ implementation that leads to denial of service for new DoQ clients. This vulnerability needs Unbound to be compiled with DoQ support ('--with-libngtcp2') and the 'quic-port' to be configured for the listening interfaces.

In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the reply in place fails to bound the reply length against the destination buffer size. The size clamp that protects the UDP path is not applied on the TCP path, so a reply larger than 65504 bytes is shifted forward by 48 bytes inside a buffer of capacity equal to 'msg-buffer-size', writing past the end of the heap allocation. A single malicious encrypted query crashes the resolver and lead to denial of service. This vulnerability needs Unbound to be compiled with DNSCrypt support ('--enable-dnscrypt') and the 'dnscrypt:' clause to be configured and enabled for the listening interfaces.

'dns-error-reporting: yes' leads to stack buffer overflow

RRSIGs with too few labels can lead to bypass of DNSSEC wildcard validation

In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.

Last updated 24 September 2026

DNS-over-QUIC (DoQ) path-migration can lead to use-after-free on multi-threaded deployments.

When Routinator encounters a CRL with many entries, it may hang or run out of memory. If Routinator encounters a CRL file with the wrong encoding, it may exit.