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ISC BIND 9 CVE-2026-11331

| EUVDEUVD-2026-47706 HIGH
Improper Filtering of Special Elements (CWE-790)
2026-07-22 isc GHSA-8p39-mp4q-99c8
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:H/I:N/A:N
vuln.today AI
8.2 HIGH

Remote unauthenticated crafted query (AV:N/AC:L/PR:N/UI:N); primary impacts are daemon crash (A:H) and RPZ filtering bypass (I:L), with no data disclosure (C:N).

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/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
High
Integrity
None
Availability
None

Lifecycle Timeline

2
Analysis Generated
Jul 22, 2026 - 15:17 vuln.today
CVE Published
Jul 22, 2026 - 14:10 cve.org
HIGH 7.5

DescriptionCVE.org

An attacker who knows (or guesses) that a resolver uses RPZ with wildcard CNAME policies can craft query names long enough to trigger a NAMETOOLONG error condition during RPZ processing. This is not handled correctly and may lead to defeating the RPZ rule. It also may lead to an unexpected exit of the BIND 9 software. This issue affects BIND 9 versions 9.16.0 through 9.18.50, 9.20.0 through 9.20.24, 9.21.0 through 9.21.23, 9.16.8-S1 through 9.18.50-S1, and 9.20.9-S1 through 9.20.24-S1.

AnalysisAI

RPZ policy bypass and remote denial-of-service in ISC BIND 9 resolvers lets unauthenticated attackers defeat Response Policy Zone protections or crash the daemon by sending queries with names long enough to trigger a NAMETOOLONG condition during RPZ processing. Affected are BIND 9.16.0-9.18.50, 9.20.0-9.20.24, 9.21.0-9.21.23 and the corresponding -S (subscription) editions, but only where RPZ is configured with wildcard CNAME policies. No public exploit identified at time of analysis; the vendor (ISC) has released fixed builds 9.20.26 and 9.21.24.

Technical ContextAI

BIND 9 is the reference implementation of DNS and one of the most widely used recursive resolver/authoritative servers (cpe:2.3:a:isc:bind_9). Response Policy Zones (RPZ) are a DNS firewall mechanism that let operators rewrite or block answers for malicious domains; wildcard CNAME policies (e.g. *.evil.example CNAME rpz-drop) apply an action across a whole subtree. The flaw is classed as CWE-790 (Improper Filtering of Special Elements): during RPZ evaluation, constructing the synthesized/expanded name from an attacker-supplied very long query name overruns the DNS 255-octet name limit and raises a NAMETOOLONG error that the RPZ code path does not handle correctly. The mishandling either aborts RPZ evaluation before the policy is applied (bypass) or propagates into an assertion/unexpected termination of the named process.

RemediationAI

Vendor-released patch: upgrade to BIND 9.20.26 (https://downloads.isc.org/isc/bind9/9.20.26) or 9.21.24 (https://downloads.isc.org/isc/bind9/9.21.24), per ISC advisory https://kb.isc.org/docs/cve-2026-11331; subscription-edition users should obtain the equivalent -S build from ISC support. If patching cannot be done immediately, the most direct compensating control is to remove or rewrite wildcard CNAME entries in RPZ policy zones (replacing wildcard CNAME actions with explicit per-name policies or non-CNAME actions such as CNAME rpz-drop/rpz-passthru on specific labels), which eliminates the vulnerable code path at the cost of coarser policy coverage; alternatively, temporarily disabling RPZ (response-policy) removes the exposure entirely but also removes DNS-firewall protection, so weigh that trade-off. Restrict recursive service to trusted clients via allow-query/allow-recursion ACLs to limit who can send the crafted queries.

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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-2026-11331 vulnerability details – vuln.today

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