CVE-2026-13204 in BIND 9
Summary
by MITRE • 07/22/2026
If a provably insecure domain is covered by both an NSEC and NSEC3 record at the parent, and there exist an RRSIG for only one of these types, then BIND may exit unexpectedly with an assertion while validating this proof. This issue affects BIND 9 versions 9.11.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, 9.11.3-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.24-S1.
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Analysis
by VulDB Data Team • 07/22/2026
This vulnerability represents a critical assertion failure in the BIND DNS server implementation that occurs during DNSSEC validation when processing certain malformed or inconsistent NSEC and NSEC3 record combinations. The flaw manifests when a domain that is provably insecure contains both NSEC and NSEC3 records at the parent zone level, with only one of these record types bearing an RRSIG signature. This specific combination triggers an unexpected assertion within BIND's validation logic, causing the server to terminate abruptly and potentially disrupting DNS services for affected domains.
The technical root cause stems from BIND's internal handling of DNSSEC proof validation where the software encounters a state inconsistency when validating insecure delegations that contain conflicting record type signatures. When NSEC and NSEC3 records coexist for the same provably insecure domain, and only one carries a valid RRSIG, the assertion failure occurs during the cryptographic validation process. This behavior represents a classic case of improper error handling in cryptographic protocol implementations, where the software fails to gracefully handle edge cases in DNSSEC proof construction rather than continuing normal operation or returning appropriate error codes.
The operational impact of this vulnerability extends beyond simple service disruption as it can affect the availability and reliability of DNS infrastructure across multiple domains. When BIND servers encounter this specific pattern during validation, they may crash or restart unexpectedly, potentially causing DNS resolution failures for clients attempting to access affected domains. This is particularly concerning in production environments where DNS stability is critical, as the crash behavior could be exploited to cause denial-of-service conditions against authoritative name servers, making it a significant concern for network infrastructure operators.
Mitigation strategies should focus on immediate patching of affected BIND versions to address the assertion failure and implementing proper monitoring for unusual crash patterns. Organizations should ensure their BIND installations are updated to versions that resolve this specific validation logic error, which typically involves upgrading beyond the affected version ranges mentioned in the vulnerability description. Additionally, network administrators should implement robust monitoring solutions to detect unexpected BIND process terminations and consider implementing redundant DNS infrastructure to minimize service impact from such crashes. This vulnerability aligns with CWE-617: Reachable Assertion, which specifically addresses situations where assertions can be reached through malicious input or conditions, and may map to ATT&CK technique T1499.004: Endpoint Denial of Service - File System Consumption, as the crash behavior can effectively consume system resources through process restart cycles.