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.

When parsing an AS range in Routinator, if the maximum value of the range is smaller than the minimum value of the range, Routinator will never reach the maximum value and run out of memory.

Routinator runs out of open connections on the HTTP server when many connections are opened but never closed, leaving the HTTP server unavailable. This condition can be triggered maliciously by an attacker by opening a large number of connections to the HTTP server.

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

Routinator exits when an rsync URI for a file obtained over RRDP contains a path that cannot be stored on disk, such as too long file names, and folder names that overlap with existing file names.

Routinator stores a newly-retrieved TA certificate via HTTPS in cache without validation, potentially overwriting a known good TA certificate even if validation fails.

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.

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.

Routinator runs out of memory when the JSON output is requested many times concurrently. This condition can be triggered maliciously by an attacker by opening a large number of connections to the HTTP server. Additionally Routinator runs into a stack overflow and exits when a payload item with too much metadata is discarded at once.

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

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

NLnet Labs Unbound up to and including version 1.26.1 limits compression-pointer traversal for each individual domain-name operation but has no aggregate inbound decompression-work budget. Many chained compression pointers in a message results in a lot of CPU usage following them. A malicious actor with recursive-query access and control of an ordinarily delegated authority that serves specially crafted replies can exploit the vulnerability and degrade Unbound's general performance.

When NLnet Labs Unbound up to and including version 1.26.1 is configured with both a root trust anchor and an additional 'trust-anchor:' for an island-of-security zone whose parent is provably insecure under the root chain, a malicious actor who can deliver one forged NXDOMAIN response for a name inside the island, with the NSEC/SOA RRSIG 'SignerName' set to the insecure parent, tricks Unbound's validator to use the root trust anchor instead, and consecutively the insecure parent, thus causing that record to be treated as insecure and denying existence for records in the trust island.

When NLnet Labs Unbound 1.0.1 up to and including version 1.26.1 is configured with both a root trust anchor and an additional 'trust-anchor:' for an island-of-security zone whose parent is provably insecure under the root chain, a malicious actor with a forged NSEC reply with the SOA bit cleared can trick Unbound to treat the configured trust island as insecure. This happens because the DNSSEC validator in Unbound accepts and caches the NSEC insecure response bypassing the RRSIG validation that the validator was supposed to do. The acceptance of the NSEC record at the trust anchor apex was allowed due to and old fix for type DS and NSEC queries from clients when trust anchor for that name existed.

In NLnet Labs Unbound up to and including version 1.26.1, an observable cache-level side-channel can be exposed with 'unwanted-reply-threshold > 0' configurations (not a default configuration). If a response-like UDP datagram reaches the upstream source port currently used by a recursive query, but its TXID does not match any pending query, Unbound counts the packet as an unwanted reply. When the accumulated count reaches the configured threshold, Unbound clears the worker's RRset cache and message cache. This cache clear action does not destroy the current upstream UDP pending query. Therefore, an external observer can distinguish whether a candidate port matches the current upstream source port by checking whether an existing cached item has been cleared. This is a cache side-channel vulnerability that can be used to probe the upstream source port. Although the attack is not feasible on default configurations and the suggested value (10 million) makes it an ureliable attack on a public resolver, in scenarios where the attacker can keep a concurrent query window alive, the attacker can first filter the source port and then perform birthday-style guessing against the TXID, making cache poisoning a feasible attack path.

Several vulnerabilities were found in NSD. The overview of the vulnerabilities with a brief description is:

CVE-2026-101337 - severity: HIGH RCE class stack overwrite from specially formatted base64 RDATA field

CVE-2026-101338 - severity: HIGH RCE class stack overwrite from a crafted and formatted SVCB or HTTPS RR

CVE-2026-101339 - severity: HIGH RCE class stack overwrite from a crafted and formatted HIP RR

CVE-2026-101341 - severity: HIGH RCE class stack overwrite from specially formatted TXT-DATA RDATA field

The patches are tested to apply/work on 4.15.2.

Best regards, -- Willem, on behalf of the NSD team.

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).

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).

In NLnet Labs Unbound up to and including 1.26.0, a vulnerability was found in the DNSSEC validator that enables denial of service and possible remote code execution as a result of digesting DNSKEYs. A DNSKEY with an owner compression pointer to its own RDATA can overflow the digest buffer. Remote code execution is possible through attacker controlled data. An adversary can exploit the vulnerability by controlling a malicious zone and querying a vulnerable Unbound.

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.

In NLnet Labs Unbound up to and including 1.26.0, a vulnerability was found in that can progressively corrupt heap memory and under certain systems and compilation options could lead to remote code execution. The vulnerability starts when CNAME synthesis during an upstream response needs to enforce(rewrite) a max TTL value in the packet buffer. Coupled with a compression pointer that points to the overwritten value and invalidates the domain name, it leads to an error path that does not properly move the buffer position and allows for the heap buffer overflow. Since this is heavily reliant on heap memory layout, results are memory corruption that eventually leads to a crash and under specific systems and compilation options remote code execution.

Last updated 24 September 2026

NLnet Labs Unbound 1.12.0 up to and including 1.26.0 has a use-after-free vulnerability when compiled for DNS-over-HTTPs support with '--with-libnghttp2'. During failure code paths (i.e., RPZ drop query, jostle due to heavy traffic), a dropped DoH stream brings down the whole DoH session and does not account properly for other DoH streams in the same session. This leads to use-after-free in those code paths. If the prerequisites are satisfied (possible RPZ drop or heavy client traffic), a malicious actor can trigger the vulnerability with a single DoH connection and the appropriate traffic. Impact is limited as the reads are not user controlled and the use-after-free leads to early returns. However, a hardened allocator can catch the use-after-free and controllably terminate the process resulting to denial of service.

CNAME synthesis could lead to heap corruption

Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY

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.

NLnet Labs Unbound 1.22.0 up to and including 1.26.1, has a use-after-free vulnerability when compiled for DNS-over-QUIC support with '--with-libngtcp2'. Each DoQ stream owns an output buffer that holds the DNS response. ngtcp2's retransmission buffer keeps a shallow pointer into the output buffer for as long as a STREAM frame may be resent. On a client RESETSTREAM, the output buffer is freed but ngtcp2 still holds the matching retransmission entries. The next PTO timeout makes ngtcp2 re-encode the STREAM frame and copy from the freed buffer. A malicious actor that can query Unbound over DoQ and that withholds ACKs, sends RESETSTREAM, and waits for PTO, reaches this use-after-free with no privilege. This leads to retransmissions against freed memory and eventually an abnormal server exit under a 20-query spray.

In NLnet Labs Unbound 1.13.2 up to and including 1.26.1, a vulnerability in ZONEMD configured zones (zonemd-check: yes) which are located below (but not at) a trust anchor allow for an attack window where (tampered with) zone contents are served (or stored to disk) prior to the ZONEMD integrity check. This is caused by the needed DS/DNSKEY asynchronous resolution that needs to happen before the ZONEMD check completes. If a zonefile is written to disk (zonefile: option) while the ZONEMD check failed, the tampered data are reloaded on startup and available until ZONEMD verification concludes again. If verification fails, the data is not served any more but still persists on disk for future reloads.

Hi there,

(The official announcement can be found at: https://community.nlnetlabs.nl/t/unbound-1-26-1-released/3463)

Several vulnerabilities were found in Unbound. The overview of the vulnerabilities with a brief description is:

CVE-2026-81642 - severity: CRITICAL CVE-2026-81634 - severity: HIGH Possible heap buffer overflow during DNSSEC canonicalization

CVE-2026-82717 - severity: HIGH CNAME synthesis could lead to heap corruption

CVE-2026-77955 - severity: MEDIUM Possible ZONEMD verification bypass window

CVE-2026-78227 - severity: MEDIUM Use-after-free in DoQ stream output buffer on reset re-transmission

CVE-2026-80225 - severity: MEDIUM CVE-2026-82720 - severity: MEDIUM Use-after-free in DoH stream cleanup code path

CVE-2026-85501 - severity: MEDIUM CVE-2026-77860 - severity: LOW 'serve-expired' can bypass Unbound 'wait-limit'

More information about the vulnerabilities can be found at: https://nlnetlabs.nl/projects/unbound/security-advisories/

Best regards, -- Yorgos, on behalf of the Unbound team.

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