---
id: CVE-2026-5950
title: >-
  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 …
summary: >-
  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 …
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'
cwe:
  - CWE-606
vendor: isc
product: bind
affected:
  - 'bind >= 9.18.36, < 9.18.49'
  - 'bind >= 9.20.8, < 9.20.23'
  - 'bind >= 9.21.7, < 9.21.21'
patched:
  - bind 9.21.21
published: '2026-05-20'
updated: '2026-07-23'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-5950'
references:
  - url: 'https://downloads.isc.org/isc/bind9/9.18.49'
    label: security-officer@isc.org
  - url: 'https://downloads.isc.org/isc/bind9/9.20.23'
    label: security-officer@isc.org
  - url: 'https://downloads.isc.org/isc/bind9/9.21.22'
    label: security-officer@isc.org
  - url: 'https://kb.isc.org/docs/cve-2026-5950'
    label: security-officer@isc.org
tags:
  - nvd
  - exploit-available
epss: 0.0066
epssPercentile: 0.50176
ingestedAt: '2026-07-23T12:17:54.932Z'
exploits:
  github: 1
  githubRepos:
    - 'https://github.com/billybaraja/cve-2026-5950-bind9-resolver-dos'
  checkedAt: '2026-09-24T07:53:10.299Z'
exploitAvailable: true
---

## Overview

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

- `bind >= 9.18.36, < 9.18.49`
- `bind >= 9.20.8, < 9.20.23`
- `bind >= 9.21.7, < 9.21.21`

## Remediation

Upgrade past the affected range:

- `bind 9.21.21`