---
id: CVE-2026-5947
title: >-
  Undefined behavior may result due to a race condition leading to a
  use-after-free violation
summary: >-
  Undefined behavior may result due to a race condition leading to a
  use-after-free violation.  If BIND receives an incoming DNS message signed
  with SIG(0), it begins work to validate that signature.  If, during that
  validation, the "recur…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-362
  - CWE-416
  - CWE-367
vendor: isc
product: bind
affected:
  - 'bind >= 9.20.0, < 9.20.23'
  - 'bind >= 9.21.0, < 9.21.22'
patched:
  - bind 9.21.22
published: '2026-05-20'
updated: '2026-07-23'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-5947'
references:
  - 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-2026-5947'
    label: security-officer@isc.org
  - url: 'https://access.redhat.com/errata/RHSA-2026:7412'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/security/cve/CVE-2026-5947'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2479772'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
tags:
  - nvd
epss: 0.01387
epssPercentile: 0.70617
ingestedAt: '2026-07-23T12:17:54.909Z'
---

## Overview

Undefined behavior may result due to a race condition leading to a use-after-free violation.  If BIND receives an incoming DNS message signed with SIG(0), it begins work to validate that signature.  If, during that validation, the "recursive-clients" limit is reached (as would occur during a query flood), and that same DNS message is discarded per the limit, there is a brief window of time while the SIG(0) validation may attempt to read the now-discarded DNS message.
This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1.
BIND 9 versions 9.18.28 through 9.18.49 and 9.18.28-S1 through 9.18.49-S1 are NOT affected.

## Affected

- `bind >= 9.20.0, < 9.20.23`
- `bind >= 9.21.0, < 9.21.22`

## Remediation

Upgrade past the affected range:

- `bind 9.21.22`