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ISC BIND 9 CVE-2026-13321

| EUVDEUVD-2026-47713 HIGH
Origin Validation Error (CWE-346)
2026-07-22 isc GHSA-36gp-wrgh-j78w
8.6
CVSS 3.1 · Vendor: isc
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Severity by source

Vendor (isc) PRIMARY
8.6 HIGH
AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
vuln.today AI
8.6 HIGH

Network-reachable unauthenticated attacker serving signed responses (AV:N/AC:L/PR:N/UI:N); forged cross-zone denial breaks another zone's integrity, giving S:C and I:H with no confidentiality or availability loss.

3.1 AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N
SUSE
HIGH
qualitative
Red Hat
8.6 HIGH
qualitative

Primary rating from Vendor (isc).

CVSS VectorVendor: isc

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
None
Integrity
High
Availability
None

Lifecycle Timeline

2
Analysis Generated
Jul 22, 2026 - 15:19 vuln.today
CVE Published
Jul 22, 2026 - 14:16 cve.org
HIGH 8.6

DescriptionCVE.org

The BIND resolver accepts validly-signed NSEC records where the "Next Domain Name" field points outside the signer's zone. 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.

AnalysisAI

DNSSEC validation bypass in ISC BIND 9 resolvers (9.11.0 through 9.21.23 and S-editions) allows an attacker controlling a signed zone to inject validly-signed NSEC records whose 'Next Domain Name' field points outside the signer's own zone, letting forged proofs of non-existence be applied to names the zone was never authorized to speak for. Because BIND fails to enforce that the NSEC chain stays within the signer's authority, an attacker can assert that arbitrary names in other zones do not exist, poisoning resolver behavior across zone boundaries (CVSS 8.6, Scope:Changed, integrity impact). There is no public exploit identified at time of analysis and the issue is not in CISA KEV.

Technical ContextAI

The vulnerability lives in BIND 9's DNSSEC validation path for NSEC records, the authenticated-denial-of-existence mechanism defined in RFC 4034/4035. Each NSEC record cryptographically links one existing name to the next existing name in canonical order within a zone via its 'Next Domain Name' RDATA field, forming a chain that proves which names do and do not exist. The affected products are ISC BIND 9 (cpe:2.3:a:isc:bind_9), specifically the full range 9.11.0-9.18.50, 9.20.0-9.20.24, 9.21.0-9.21.23 plus the subscription '-S' editions. The root cause maps to CWE-346 (Origin Validation Error): BIND validates that the NSEC record is correctly signed but does not verify that the 'Next Domain Name' target actually falls within the signer's delegated namespace, so a signature that is cryptographically valid for zone A is honored even when it makes assertions about names belonging to zone B. This breaks the trust boundary that DNSSEC is meant to enforce between independently signed zones.

RemediationAI

Vendor-released patch: upgrade to BIND 9.20.26 or 9.21.24, published by ISC at https://downloads.isc.org/isc/bind9/9.20.26 and https://downloads.isc.org/isc/bind9/9.21.24 respectively; subscription-edition users should obtain the corresponding fixed -S build from ISC support. Consult the advisory at https://kb.isc.org/docs/cve-2026-13321 for the exact branch mapping before upgrading. Because this is a validation-logic flaw with no standalone configuration toggle, there is no clean feature-level workaround that preserves DNSSEC guarantees; disabling DNSSEC validation (dnssec-validation no;) would silence the specific NSEC cross-zone acceptance but at the cost of removing all DNSSEC protection, which is a net security downgrade and not recommended. The practical path is to prioritize the version upgrade, and in the interim restrict which upstream authoritative servers your resolver will trust and monitor for anomalous NXDOMAIN/non-existence responses affecting unrelated zones.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise Desktop 15 SP7 SUSE Linux Enterprise Module for Basesystem 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed
SUSE Linux Enterprise Module for Server Applications 15 SP7 Fixed
openSUSE Leap 16.0 Fixed
openSUSE Tumbleweed Fixed

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CVE-2026-13321 vulnerability details – vuln.today

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