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BIND 9 CVE-2026-11605

| EUVDEUVD-2026-47707 HIGH
Incorrect Behavior Order: Early Amplification (CWE-408)
2026-07-22 isc GHSA-qhh7-j7w3-xfxq
7.5
CVSS 3.1 · Vendor: isc
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Severity by source

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

Remotely reachable, low-complexity, unauthenticated attack against a validating resolver with pure availability impact and no confidentiality or integrity loss, matching the vendor 7.5 rating.

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

Primary rating from Vendor (isc).

CVSS VectorVendor: isc

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

Lifecycle Timeline

2
Analysis Generated
Jul 22, 2026 - 15:17 vuln.today
CVE Published
Jul 22, 2026 - 14:11 cve.org
HIGH 7.5

DescriptionCVE.org

The issue is a resource exhaustion vulnerability associated with DNSSEC validation. BIND always validates all RRSIG records in an answer, even if they are not strictly needed. A query to an authoritative server/zone which returns many valid but superfluous RRSIG records causes the validator to waste disproportionate CPU time. This issue affects BIND 9 versions 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, and 9.20.9-S1 through 9.20.24-S1.

AnalysisAI

Denial of service in ISC BIND 9 resolvers (9.20.0-9.20.24, 9.21.0-9.21.23, and 9.20.9-S1-9.20.24-S1) lets remote unauthenticated attackers exhaust CPU by luring a validating resolver to query an authoritative zone that returns many valid-but-superfluous RRSIG records, which BIND always validates even when unnecessary. The CVSS 7.5 vector (AV:N/AC:L/PR:N/UI:N/A:H) reflects an availability-only impact with no confidentiality or integrity loss. There is no public exploit identified at time of analysis and it is not in CISA KEV, but ISC has released fixed builds (9.20.26 and 9.21.24).

Technical ContextAI

The affected component is ISC BIND 9 (cpe:2.3:a:isc:bind_9), the most widely deployed open-source DNS server, operating here in its validating-resolver role. The root cause maps to CWE-408 (Incorrect Behavior Order: Early Amplification): during DNSSEC validation BIND cryptographically verifies every RRSIG record present in an answer, rather than stopping once a sufficient valid signature has been found. Because RRSIG verification involves relatively expensive public-key cryptographic operations, an answer padded with numerous valid-but-not-strictly-needed RRSIGs forces the validator to perform disproportionate CPU work per query, turning a small crafted response into an asymmetric resource-consumption (amplification) condition. The vulnerability only manifests when DNSSEC validation is active, which is the default posture for modern recursive BIND deployments.

RemediationAI

Upgrade to a fixed ISC release: BIND 9.20.26 (https://downloads.isc.org/isc/bind9/9.20.26) for the 9.20 stable branch or BIND 9.21.24 (https://downloads.isc.org/isc/bind9/9.21.24) for the 9.21 branch; subscription-edition users on the 9.20.x-S1 line should obtain the corresponding patched S-edition build from ISC support, per the advisory at https://kb.isc.org/docs/cve-2026-11605. Vendor-released patch: 9.20.26 and 9.21.24. If immediate patching is not possible, compensating controls include restricting recursion to trusted client networks (allow-recursion / views) so untrusted parties cannot drive arbitrary lookups through the validator, and rate-limiting or fronting the resolver with query controls to cap CPU spent per client; as a last resort DNSSEC validation could be disabled (dnssec-validation no), but this removes protection against DNS spoofing/cache poisoning and is strongly discouraged. Monitor named CPU utilization and consider resolver redundancy so a single overloaded instance does not cause a full outage.

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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-2026-11605 vulnerability details – vuln.today

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