Unbounded resend loop in BIND 9 resolver

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Summary

CVECVE-2026-5950
StatePUBLISHED
Assignerisc
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-20 13:16:40 UTC
Updated2026-05-21 15:24:34 UTC
DescriptionAn 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.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS: 0.000910000 probability, percentile 0.255220000 (date 2026-05-27)

Problem Types: CWE-606 | CWE-606 CWE-606 Unchecked Input for Loop Condition

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNADECLARED5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

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

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Isc Bind All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA ISC BIND 9 affected 9.18.36 9.18.48 custom Not specified
CNA ISC BIND 9 affected 9.20.8 9.20.22 custom Not specified
CNA ISC BIND 9 affected 9.21.7 9.21.21 custom Not specified
CNA ISC BIND 9 affected 9.18.36-S1 9.18.48-S1 custom Not specified
CNA ISC BIND 9 affected 9.20.9-S1 9.20.22-S1 custom Not specified

References

ReferenceSourceLinkTags
downloads.isc.org/isc/bind9/9.21.22 [email protected] downloads.isc.org Patch
kb.isc.org/docs/cve-2026-5950 [email protected] kb.isc.org Vendor Advisory
downloads.isc.org/isc/bind9/9.20.23 [email protected] downloads.isc.org Patch
downloads.isc.org/isc/bind9/9.18.49 [email protected] downloads.isc.org Patch
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: ISC would like to thank Billy Baraja (BielraX) for bringing this vulnerability to our attention. (en)

Additional Advisory Data

Solutions

CNA: Upgrade to the patched release most closely related to your current version of BIND 9: 9.18.49, 9.20.23, 9.21.22, 9.18.49-S1, or 9.20.23-S1.

Workarounds

CNA: No workarounds known.

Exploits

CNA: We are not aware of any active exploits.

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