CVE-2026-5950
Analyzed Analyzed - Analysis Complete
Denial of Service in BIND 9 Resolver

Publication date: 2026-05-20

Last updated on: 2026-05-21

Assigner: Internet Systems Consortium (ISC)

Description
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.
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Meta Information
Published
2026-05-20
Last Modified
2026-05-21
Generated
2026-06-10
AI Q&A
2026-05-20
EPSS Evaluated
2026-06-08
NVD
CVE-2026-5950
EUVD
EUVD-2026-31109
Affected Vendors & Products
Showing 3 associated CPEs
Vendor Product Version / Range
isc bind From 9.18.36 (inc) to 9.18.49 (exc)
isc bind From 9.20.8 (inc) to 9.20.23 (exc)
isc bind From 9.21.7 (inc) to 9.21.21 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
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.
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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

Executive Summary

CVE-2026-5950 is a vulnerability in the BIND 9 DNS resolver where an unbounded resend loop occurs in the resolver's state machine during bad-server handling.

This happens when queries trigger specific retry conditions, allowing a remote unauthenticated attacker to cause the resolver to repeatedly resend queries without limit.

As a result, this leads to severe resource exhaustion on the affected system.

Impact Analysis

The vulnerability can cause severe resource exhaustion on systems running vulnerable versions of the BIND 9 resolver.

This resource exhaustion could degrade system performance or availability, potentially leading to denial of service conditions.

Since the attack can be performed remotely and without authentication, it poses a risk to any exposed resolver using affected BIND 9 versions.

Mitigation Strategies

The immediate step to mitigate this vulnerability is to upgrade BIND to a patched version.

  • Upgrade to BIND 9.18.49, 9.20.23, or 9.21.22, or their Supported Preview Edition equivalents.

No known workarounds exist, so upgrading is the recommended and effective mitigation.

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