Unbounded Resend Loop Vulnerability in BIND 9 Resolver by ISC
CVE-2026-5950

5.3MEDIUM

Key Information:

Vendor

Isc
Status
Bind 9
Vendor
CVE Published:
20 May 2026

Badges

👾 Exploit Exists

What is CVE-2026-5950?

A vulnerability exists in the BIND 9 resolver state machine that can lead to an unbounded resend loop during the handling of bad servers. This allows remote unauthenticated attackers to send specially crafted queries that trigger retries, potentially leading to severe resource exhaustion on affected systems. This issue impacts specific versions of BIND 9, including 9.18.36 to 9.18.48, 9.20.8 to 9.20.22, and 9.21.7 to 9.21.21.

Affected Version(s)

BIND 9 9.18.36 <= 9.18.48

BIND 9 9.20.8 <= 9.20.22

BIND 9 9.21.7 <= 9.21.21

References

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

CVSS V3.1

Score:
5.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

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