Vulnerability · Published May 20, 2026 · Assigned by isc
CVE-2026-5950Unbounded resend loop in BIND 9 resolver
Medium 5.3
In plain English
A medium-severity security flaw in BIND 9 from ISC. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 52% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.20 | bind | 9.18.49-r0 | ALPINE-CVE-2026-5950 |
| Alpine:v3.21 | bind | 9.18.49-r0 | ALPINE-CVE-2026-5950 |
| Alpine:v3.22 | bind | 9.20.23-r0 | ALPINE-CVE-2026-5950 |
| Alpine:v3.23 | bind | 9.20.23-r0 | ALPINE-CVE-2026-5950 |
| Alpine:v3.24 | bind | 9.20.23-r0 | ALPINE-CVE-2026-5950 |
| Debian:12 | bind9 | 1:9.18.49-1~deb12u2 | DEBIAN-CVE-2026-5950 |
| Debian:13 | bind9 | 1:9.20.23-1~deb13u1 | DEBIAN-CVE-2026-5950 |
| Debian:14 | bind9 | 1:9.20.23-1 | DEBIAN-CVE-2026-5950 |
| Ubuntu:22.04:LTS | bind9 | 1:9.18.39-0ubuntu0.22.04.4 | UBUNTU-CVE-2026-5950 |
| Ubuntu:24.04:LTS | bind9 | 1:9.18.39-0ubuntu0.24.04.5 | UBUNTU-CVE-2026-5950 |
| Ubuntu:25.10 | bind9 | 1:9.20.11-1ubuntu2.4 | UBUNTU-CVE-2026-5950 |
| Ubuntu:26.04:LTS | bind9 | 1:9.20.18-1ubuntu2.1 | UBUNTU-CVE-2026-5950 |
| Ubuntu:22.04:LTS | bind9-libs | no fix listed | UBUNTU-CVE-2026-5950 |
| Ubuntu:24.04:LTS | isc-dhcp | no fix listed | UBUNTU-CVE-2026-5950 |
| Ubuntu:25.10 | isc-dhcp | no fix listed | UBUNTU-CVE-2026-5950 |
| Ubuntu:26.04:LTS | isc-dhcp | no fix listed | UBUNTU-CVE-2026-5950 |
Affected products (as reported)
Weakness: CWE-606 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L