CVE-2026-46582
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk9th percentile - higher than 9% 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-2026-85501Medium
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.
- CVE-2026-80225Medium
In NLnet Labs Unbound up to and including 1.26.0, a degradation of service vulnerability is present in the TCP/DoT reading procedure where there is no limit on consecutive reads. A malicious actor that can stream and sustain a rate of distinct uncached names over the TCP/DoT connection monopolizes a single worker's entire event loop for as long as its writes stay ahead of the drain.
- CVE-2026-78227Medium
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 holding the DNS response, and ngtcp2's retransmission buffer keeps a shallow pointer into it. On client RESET_STREAM, the output buffer is freed but ngtcp2 still holds matching retransmission entries, leading to use-after-free on next PTO. An unprivileged attacker can trigger this by querying over DoQ, withholding ACKs, sending RESET_STREAM, and waiting for PTO, causing abnormal server exit.
- CVE-2026-77955Medium
In NLnet Labs Unbound 1.13.2 up to and including 1.26.1, in zones with ZONEMD enabled (zonemd-check: yes) located below a trust anchor, there is an attack window where tampered zone contents are served (or stored to disk) prior to the ZONEMD integrity check. This is caused by the needed DS/DNSKEY asynchronous resolution before the ZONEMD check completes. If a zonefile is written to disk while the ZONEMD check failed, the tampered data are reloaded on startup and available until ZONEMD verification concludes again.
- CVE-2026-77860Low
In NLnetLabs Unbound 1.20.0 up to and including 1.26.0, a vulnerability on the 'serve-expired' code path can cause a double decrement on the 'wait-limit' counter per client IP essentially bypassing one of the counter measures that was introduced for DNSBomb (CVE-2024-33655). A malicious actor can exploit this by controlling an authoritative zone with short TTL, so cached entries expire quickly. Each 'slow' query, one the attacker's authoritative never answers, is followed by one query for an expired cached name, which is answered immediately via the 'serve-expired' path and decrements the counter twice. This second query was named 'pump'. By alternating slow queries and pumps, the attacker keeps the per-client counter at or below the configured 'wait-limit' indefinitely, and can hold an arbitrary number of pending queries from a single source IP, up to the global mesh quota (num-queries-per-thread); eventually bypassing one of the counter measures introduced for DNSBomb (CVE-2024-33655). This vulnerability is present on the 'serve-expired' code path.
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