---
id: CVE-2019-16866
title: >-
  Unbound before 1.9.4 accesses uninitialized memory, which allows remote
  attackers to trigger a crash via a crafted NOTIFY query
summary: >-
  Unbound before 1.9.4 accesses uninitialized memory, which allows remote
  attackers to trigger a crash via a crafted NOTIFY query. The source IP address
  of the query must match an access-control rule.
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-755
  - CWE-908
  - CWE-822
vendor: nlnetlabs
product: unbound
affected:
  - unbound < 1.9.4
  - ubuntu_linux = 19.04
patched:
  - unbound 1.9.4
published: '2019-10-03'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T21:17:16.327'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2019-16866'
references:
  - url: 'https://github.com/NLnetLabs/unbound/blob/release-1.9.4/doc/Changelog'
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/E65NCWZZB2D75ZIYWPXKMVGSGNYW4JMC/
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MLRHE7TQFAOV4MB2ELTOGESZYUL65NUJ/
    label: cve@mitre.org
  - url: 'https://nlnetlabs.nl/downloads/unbound/CVE-2019-16866.txt'
    label: cve@mitre.org
  - url: 'https://seclists.org/bugtraq/2019/Oct/23'
    label: cve@mitre.org
  - url: 'https://usn.ubuntu.com/4149-1/'
    label: cve@mitre.org
  - url: 'https://www.debian.org/security/2019/dsa-4544'
    label: cve@mitre.org
  - url: 'https://github.com/NLnetLabs/unbound/blob/release-1.9.4/doc/Changelog'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/E65NCWZZB2D75ZIYWPXKMVGSGNYW4JMC/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MLRHE7TQFAOV4MB2ELTOGESZYUL65NUJ/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://nlnetlabs.nl/downloads/unbound/CVE-2019-16866.txt'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://seclists.org/bugtraq/2019/Oct/23'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://usn.ubuntu.com/4149-1/'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://www.debian.org/security/2019/dsa-4544'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2019/cve-2019-16866.json
  - url: 'https://access.redhat.com/security/cve/CVE-2019-16866'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=1767955'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2019-16866'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2019-16866'
tags:
  - nvd
  - csaf
  - vex
  - red-hat
  - score-dispute
epss: 0.03506
epssPercentile: 0.88863
ingestedAt: '2026-10-08T22:11:53.702Z'
scores:
  nvd: 7.5
  vendor: 5.3
---

## Overview

Unbound before 1.9.4 accesses uninitialized memory, which allows remote attackers to trigger a crash via a crafted NOTIFY query. The source IP address of the query must match an access-control rule.

## Affected

- `unbound < 1.9.4`
- `ubuntu_linux = 19.04`

## Remediation

Upgrade past the affected range:

- `unbound 1.9.4`

## Vendor advisories

- **Red Hat VEX** · Low · affected: Red Hat Enterprise Linux 8 · no fix planned: Red Hat Enterprise Linux 8 · updated 2026-10-08 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2019/cve-2019-16866.json)