CVE-2026-5950

MEDIUM 5.3

Unbounded resend loop in BIND 9 resolver

CVSS Score

5.3

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-606
Vendor	isc
Product	bind 9
Published	May 20, 2026
Last Updated	May 20, 2026

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CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Affected Versions

ISC / BIND 9

9.18.36 ≤ 9.18.48 9.20.8 ≤ 9.20.22 9.21.7 ≤ 9.21.21 9.18.36-S1 ≤ 9.18.48-S1 9.20.9-S1 ≤ 9.20.22-S1

References

NVD ↗ CVE.org ↗ EPSS Data ↗

kb.isc.org: https://kb.isc.org/docs/cve-2026-5950 downloads.isc.org: https://downloads.isc.org/isc/bind9/9.18.49 downloads.isc.org: https://downloads.isc.org/isc/bind9/9.20.23 downloads.isc.org: https://downloads.isc.org/isc/bind9/9.21.22

Credits

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