# CVE-2019-16866: Null dereference in n/a

> Remote attackers can crash the Unbound DNS resolver by sending a crafted NOTIFY query from an allowed IP address.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 3 Oct 2019
- **Updated:** 8 Oct 2026
- **Also known as:** ALPINE-CVE-2019-16866, DEBIAN-CVE-2019-16866, DSA-4544-1, GHSA-gg25-v243-f7cq, MGASA-2019-0317

## What is CVE-2019-16866?

CVE-2019-16866 is a high-severity vulnerability in Canonical Ubuntu Linux, published on 3 Oct 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-908 (Use of Uninitialized Resource), CWE-755 (Improper Handling of Exceptional Conditions)

## Which versions are affected by CVE-2019-16866?

It affects 2 products.


Products: Canonical Ubuntu Linux, Nlnetlabs Unbound.

## How do I fix CVE-2019-16866?

Upgrade to a fixed version.

## Is CVE-2019-16866 being exploited?

There is no known exploitation of CVE-2019-16866 in the wild and no public exploit code.

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2020-11651](https://insights.sbomify.com/CVE-2020-11651/): SaltStack Salt Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2020-7247](https://insights.sbomify.com/CVE-2020-7247/): OpenSMTPD Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2019-16928](https://insights.sbomify.com/CVE-2019-16928/): Exim Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2018-6789](https://insights.sbomify.com/CVE-2018-6789/): Exim Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2015-2590](https://insights.sbomify.com/CVE-2015-2590/): Oracle Java SE and Java SE Embedded Remote Code Execution (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-16866 and fix it if it is affected.

What it is: CVE-2019-16866 is a high-severity vulnerability in Canonical Ubuntu Linux, published on 3 Oct 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2019-16866 in the wild and no public exploit code.

Affected product: Canonical Ubuntu Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2019-16866/ (Markdown: https://insights.sbomify.com/CVE-2019-16866/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-16866
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-16866
- OSV: https://osv.dev/vulnerability/CVE-2019-16866

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From sbomify Insights: https://insights.sbomify.com/CVE-2019-16866/
Summaries are generated and may contain mistakes; the official description above is the record.