What’s Vulnerable › Vulnerabilities

CVE-2026-5950: Unbounded resend loop in BIND 9 resolver

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-20 · updated 2026-07-23
• Weakness: CWE-606

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.

Affected products

• ISC BIND: from 9.18.36 before 9.18.49; from 9.20.8 before 9.20.23; from 9.21.7 before 9.21.21 — fixed in 9.18.49, 9.20.23, 9.21.21

How to fix

Upgrade to a fixed version: ISC BIND 9.18.49, 9.20.23, 9.21.21. Check the vendor advisory for mitigations.

References

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

Get alerted when CVE-2026-5950 or the next vulnerability affects your stack