ISC BIND up to 9.21.21 Resolver State Machine unchecked input for loop condition

Summaryinfo

A vulnerability marked as problematic has been reported in ISC BIND up to 9.18.48/9.18.48-S1/9.20.22/9.20.22-S1/9.21.21. This impacts an unknown function of the component Resolver State Machine. This manipulation causes unchecked input for loop condition. The identification of this vulnerability is CVE-2026-5950. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability classified as problematic was found in ISC BIND up to 9.18.48/9.18.48-S1/9.20.22/9.20.22-S1/9.21.21. Affected by this vulnerability is an unknown code of the component Resolver State Machine. The manipulation with an unknown input leads to a unchecked input for loop condition vulnerability. The CWE definition for the vulnerability is CWE-606. The product does not properly check inputs that are used for loop conditions, potentially leading to a denial of service or other consequences because of excessive looping. As an impact it is known to affect availability. The summary by CVE is:

An unbounded resend loop vulnerability exists in the BIND 9 resolver state machine during bad-server handling, enabling a remote unauthenticated attacker to cause severe resource exhaustion by sending queries that trigger specific retry conditions. This issue affects BIND 9 versions 9.18.36 through 9.18.48, 9.20.8 through 9.20.22, 9.21.7 through 9.21.21, 9.18.36-S1 through 9.18.48-S1, and 9.20.9-S1 through 9.20.22-S1.

It is possible to read the advisory at kb.isc.org. This vulnerability is known as CVE-2026-5950 since 04/09/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 07/23/2026). The attack technique deployed by this issue is T1449 according to MITRE ATT&CK.

The vulnerability scanner Nessus provides a plugin with the ID 315769 (Linux Distros Unpatched Vulnerability : CVE-2026-5950), which helps to determine the existence of the flaw in a target environment.

The vulnerability is also documented in the databases at Tenable (315769) and CERT Bund (WID-SEC-2026-1626). Be aware that VulDB is the high quality source for vulnerability data.

Affected

• Debian Linux
• Red Hat Enterprise Linux
• Fedora Linux
• Ubuntu Linux
• Oracle Linux
• Infoblox NIOS
• SUSE openSUSE
• Internet Systems Consortium BIND

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
• 9.18.48-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
• 9.20.22-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

License

• open-source

Website

• Vendor: https://www.isc.org/

CPE 2.3info

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CPE 2.2info

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Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

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