CVE-2026-5950

Unbounded resend loop in BIND 9 resolver

State: Published
Severity: 5.3 Medium
Published: May 20, 2026
Updated: May 20, 2026
Reserved: Apr 9, 2026

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.

Scores

CVSS	Score	Vector	Source
3.1	5.3 Medium	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L	isc

Weaknesses

CWE-606 Unchecked Input for Loop Condition

Affected Products

Product	Versions
BIND 9ISC	9.18.36 through 9.18.48Affected 9.20.8 through 9.20.22Affected 9.21.7 through 9.21.21Affected 9.18.36-S1 through 9.18.48-S1Affected 9.20.9-S1 through 9.20.22-S1Affected

References

CVE-2026-5950vendor-advisory
https://downloads.isc.org/isc/bind9/9.18.49patch
https://downloads.isc.org/isc/bind9/9.20.23patch
https://downloads.isc.org/isc/bind9/9.21.22patch

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