CVE-2026-46582
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk8th percentile - higher than 8% of all known CVEs
Summary
In NLnet Labs Unbound from 1.6.0 to 1.25.1, a wildcard RRset replay can be temporarily considered DNSSEC-secure based on RRSIG validation and cached. Later NSEC validation marks it as bogus, but another thread may use it for a reply, replacing a specific record with a wildcard. The attack requires a DNSSEC-signed domain and a CNAME record pointing to a sibling record of a wildcard.
Risk Assessment
A malicious actor can poison the Unbound cache, replacing records with wildcards, leading to false DNS responses and potential traffic redirection.
Recommendation
Update Unbound to a patched version and enable full NSEC validation before using cached responses.
Other vulnerabilities in Unbound
See all- CVE-2026-81642Critical
In NLnet Labs Unbound up to and including 1.26.0, a vulnerability in the DNSSEC validator enables denial of service and possible remote code execution via DNSKEY processing. A crafted DNSKEY can overflow the digest buffer.
- CVE-2026-50252Critical
In Unbound library versions 1.4.22 through 1.25.1, a vulnerability allows DNS cache poisoning attacks. The issue arises from deterministic assignment of UDP port ranges to worker threads when SO_REUSEPORT is enabled, enabling an attacker to predict the source port and reduce DNS transaction entropy.
- CVE-2026-42960Critical
NLnet Labs Unbound up to version 1.25.0 is vulnerable to cache poisoning via promiscuous records in the authority section. An attacker can inject non-NS records (e.g., MX) along with address records that Unbound caches, leading to cache poisoning. Version 1.25.1 includes a fix that disregards address records from the additional section if they are not explicitly relevant to NS records.
- CVE-2026-33278Critical
NLnet Labs Unbound from version 1.19.1 to 1.25.0 has a vulnerability in the DNSSEC validator due to a struct-assignment bug during deep copy, leading to a dangling pointer and potential code execution.
- CVE-2026-97206High
NLnet Labs Unbound, 1.22.0 up to and including version 1.26.1, contains a DNS-over-QUIC (DoQ) lifetime bug reachable by a remote DoQ client under multi-threaded operation. A client-triggered QUIC path migration can enter stream/connection cleanup while a mesh reply still retains a pointer to the DoQ stream. Cleanup frees the DoQ stream and when the pending mesh reply later completes it dereferences a stale pointer leading to a crash.
- CVE-2026-96405Medium
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 result 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.
- CVE-2026-50106Medium
In NLnet Labs Unbound up to and including version 1.26.1, when 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.
- CVE-2026-109125Medium
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). When 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 it as an unwanted reply and, upon reaching the threshold, clears the worker's RRset and message caches, allowing an external observer to distinguish whether a candidate port matches the current upstream source port.
- CVE-2026-85501Medium
NLnet Labs Unbound up to and including 1.26.0 is vulnerable to algorithmic complexity attacks (known as 'ReTrap') that cause service degradation. Attacks include TagTrap (large number of mismatched DNSKEY, RRSIG, DS records), DelegationTrap (costly iterative validation for deeply nested domains), NsecTrap (excessive invalid NSEC records), and AdditionalTrap (default validation of ADDITIONAL section).
- CVE-2026-82720Medium
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 (e.g., RPZ drop, jostle), a dropped DoH stream brings down the whole DoH session and does not account properly for other streams, leading to use-after-free. An attacker can trigger it with a single DoH connection, but impact is limited as reads are not user controlled; however, a hardened allocator can catch the use-after-free and controllably terminate the process, causing DoS.
Original NVD description (English source)
In NLnet Labs Unbound 1.6.0 up to and including 1.25.1, a replay of a wildcard rrset as another piece of data, could be briefly considered DNSSEC secure based only on the RRSIG validation and stored into cache, before later validation treats it as bogus based on NSEC validation. When the resolving thread puts secure on the rrset, and another thread that is on the serve expired path then picks up the updated rrset contents with the secure status for a reply, it can be used to change a specific record, next to a wildcard that could be covered by the wildcard, into the wildcard. A malicious actor can exploit the possible poisonous effect by having any DNSSEC-singed domain (irrelevant to the victim domain) and a CNAME wrapper record that points to a record next to a wildcard (that could be covered by the wildcard). Then quering Unbound for the wildcard sibling record would seed the secure message. A later (after expiry) query for the CNAME wrapper would need to resolve the target sibling record. If the wildcard replay is injected into the response, the wildcard rrset will update the expired sibling record with a secure status before completing proper wildcard validation with NSEC records and eventually treating the CNAME wrapper answer as bogus. The updated poisoned rrset is now secure and points to the wildcard. This vulnerability is explicit for the serve expired path and needs injection of the signed wildcard rrset without the NSEC accompanying rrset.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS