CVE-2026-5950

Medium

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.

SeverityMedium

CVSS5.3

Exploit probability—

ProductIsc Bind

PublishedMay 20, 2026

First seenMay 20, 2026

Weakness typeCWE-606CWE-606

How to fix

Update

isc bind9.18.49, 9.20.23, 9.21.21 or later

Patches

Vendor advisories

kb.isc.org/docs/cve-2026-5950

Affected products

Product	Affected versions	Fixed in
isc bind	9.18.36 ≤ v < 9.18.49, 9.20.8 ≤ v < 9.20.23, 9.21.7 ≤ v < 9.21.21	9.18.49, 9.20.23, 9.21.21

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