ISC BIND up to 9.21.23 DNSSEC Validation input validation

Summaryinfo

A vulnerability was found in ISC BIND up to 9.18.50/9.18.50-S1/9.20.24/9.20.24-S1/9.21.23. It has been classified as very critical. Affected is an unknown function of the component DNSSEC Validation. Performing a manipulation results in input validation. This vulnerability is cataloged as CVE-2026-11721. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as very critical, was found in ISC BIND up to 9.18.50/9.18.50-S1/9.20.24/9.20.24-S1/9.21.23. This affects an unknown code block of the component DNSSEC Validation. The manipulation with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

It is possible for an attacker's zone to respond to a query with an RRSIG that has a smaller number of labels than the zone in which the RRSIG is contained. This causes `named` to produce a wildcard name for a zone that is shorter than the attacker's zone, which can result in cache poisoning. For this attack to have any effect, the resolver under attack must have set `synth-from-dnssec yes;` (which is the default). 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.

It is possible to read the advisory at kb.isc.org. This vulnerability is uniquely identified as CVE-2026-11721 since 06/09/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 07/22/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Type

• Domain Name Software

Vendor

• ISC

Name

• BIND

Version

• 9.18.0
• 9.18.1
• 9.18.2
• 9.18.3
• 9.18.4
• 9.18.5
• 9.18.6
• 9.18.7
• 9.18.8
• 9.18.9
• 9.18.10
• 9.18.11
• 9.18.12
• 9.18.13
• 9.18.14
• 9.18.15
• 9.18.16
• 9.18.17
• 9.18.18
• 9.18.19
• 9.18.20
• 9.18.21
• 9.18.22
• 9.18.23
• 9.18.24
• 9.18.25
• 9.18.26
• 9.18.27
• 9.18.28
• 9.18.29
• 9.18.30
• 9.18.31
• 9.18.32
• 9.18.33
• 9.18.34
• 9.18.35
• 9.18.36
• 9.18.37
• 9.18.38
• 9.18.39
• 9.18.40
• 9.18.41
• 9.18.42
• 9.18.43
• 9.18.44
• 9.18.45
• 9.18.46
• 9.18.47
• 9.18.48
• 9.18.49
• 9.18.50
• 9.18.50-S1
• 9.20.0
• 9.20.1
• 9.20.2
• 9.20.3
• 9.20.4
• 9.20.5
• 9.20.6
• 9.20.7
• 9.20.8
• 9.20.9
• 9.20.10
• 9.20.11
• 9.20.12
• 9.20.13
• 9.20.14
• 9.20.15
• 9.20.16
• 9.20.17
• 9.20.18
• 9.20.19
• 9.20.20
• 9.20.21
• 9.20.22
• 9.20.23
• 9.20.24
• 9.20.24-S1
• 9.21.0
• 9.21.1
• 9.21.2
• 9.21.3
• 9.21.4
• 9.21.5
• 9.21.6
• 9.21.7
• 9.21.8
• 9.21.9
• 9.21.10
• 9.21.11
• 9.21.12
• 9.21.13
• 9.21.14
• 9.21.15
• 9.21.16
• 9.21.17
• 9.21.18
• 9.21.19
• 9.21.20
• 9.21.21
• 9.21.22
• 9.21.23

License

• open-source

Website

• Vendor: https://www.isc.org/

CPE 2.3info

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