CVE-2026-80274 in BIND
Summary
by MITRE • 09/16/2026
If a BIND resolver sends a query for a DNSSEC-signed authoritative zone, and the authoritative server replies with a valid wildcard answer and signed NSEC3 proof, followed by an unsigned NSEC at the same owner name, it will trigger an unexpected program exit. This issue affects BIND 9 versions 9.11.0 through 9.18.50, 9.20.0 through 9.20.27, 9.21.0 through 9.21.25, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.27-S1.
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability described involves a critical logic error in the DNSSEC validation process within BIND resolver implementations, specifically affecting versions ranging from 9.11.0 to 9.21.25 and their respective Service Pack variants up to version S1 for certain branches. This flaw manifests when a BIND resolver processes responses from an authoritative server that are technically malformed according to strict DNSSEC standards but contain valid cryptographic signatures. The specific trigger condition occurs when the authoritative server returns a wildcard answer accompanied by signed NSEC3 proofs, which serve as non-existence proofs for names between existing records, followed immediately by an unsigned NSEC record at the same owner name. In standard DNSSEC operation, NSEC and NSEC3 records are used to prove that specific domain names do not exist within a zone, thereby preventing attackers from enumerating all valid hostnames in a zone through iterative queries. The presence of both types of proofs for overlapping or conflicting data points creates an ambiguous state that the resolver's validation engine fails to handle gracefully.
From a technical perspective, this issue represents a failure in input sanitization and state machine management within the DNSSEC validator module. When the resolver encounters this contradictory set of records, it does not correctly apply the rules defined in RFC 4035 and related standards regarding how to prioritize or reject such responses. Instead of discarding the malformed response as invalid due to the inconsistency between signed NSEC3 proofs and an unsigned NSEC record at the same name, the software encounters a logic path that leads to an unexpected program exit. This behavior indicates a lack of robust error handling where critical internal assertions are likely triggered without proper exception management, causing the resolver process to terminate abruptly rather than logging the anomaly and continuing operation or returning a controlled error code to the client application.
The operational impact of this vulnerability is primarily centered on availability through denial-of-service conditions. Since BIND resolvers often run as persistent background services handling numerous concurrent queries, an unexpected exit results in the immediate loss of DNS resolution capabilities for that specific instance. If multiple resolvers are affected simultaneously or if a single resolver handles high volumes of traffic from misconfigured authoritative servers, this can lead to widespread service disruption across networks relying on BIND infrastructure. Attackers could potentially exploit this by crafting malicious responses with carefully constructed wildcard answers and mixed NSEC/NSEC3 proofs to induce crashes in targeted DNS infrastructure, effectively creating a remote denial-of-service vector without requiring authentication or prior access to the network segment hosting the authoritative server.
This vulnerability aligns with CWE-20 Improper Input Validation, as the resolver fails to adequately validate the consistency of cryptographic proof records before processing them further into its state machine. It also relates to CWE-754 Improper Check for Unusual or Exceptional Conditions, where the software does not properly handle edge cases involving conflicting DNSSEC proofs. In terms of MITRE ATT&CK mapping, this behavior can be associated with T1498 Network Denial of Service, specifically under techniques that involve resource exhaustion via application crashes rather than bandwidth saturation. The lack of graceful degradation means that even a single crafted packet from an untrusted source can disrupt service availability, highlighting the importance of strict adherence to DNSSEC specification requirements in resolver implementations.
Mitigation strategies for this vulnerability primarily involve upgrading BIND software to patched versions where the logic error has been corrected and proper exception handling is implemented for malformed DNSSEC responses. Organizations running affected versions should prioritize patching their recursive resolvers and authoritative servers that may generate such ambiguous records. Additionally, network-level defenses can be employed to monitor for unusual patterns of NSEC/NSEC3 record combinations in response traffic, although this requires deep packet inspection capabilities which are not always feasible in high-throughput environments. Security teams should also ensure that internal DNS configurations strictly adhere to RFC standards regarding the use of either NSEC or NSEC3 proofs within a single zone to prevent accidental generation of such conflicting responses by misconfigured authoritative servers. Regular auditing of DNSSEC key management and record consistency can further reduce the risk of triggering similar logic errors in other vulnerable software components.