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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.

PUBLISHED Reserved 2026-04-09 | Published 2026-05-20 | Updated 2026-05-20 | Assigner isc




MEDIUM: 5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Problem types

CWE-606 Unchecked Input for Loop Condition

Product status

Default status
unaffected

9.18.36 (custom)
affected

9.20.8 (custom)
affected

9.21.7 (custom)
affected

9.18.36-S1 (custom)
affected

9.20.9-S1 (custom)
affected

Credits

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

References

kb.isc.org/docs/cve-2026-5950 (CVE-2026-5950) vendor-advisory

downloads.isc.org/isc/bind9/9.18.49 patch

downloads.isc.org/isc/bind9/9.20.23 patch

downloads.isc.org/isc/bind9/9.21.22 patch

cve.org (CVE-2026-5950)

nvd.nist.gov (CVE-2026-5950)

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