# CVE-2018-16851: Null dereference in samba

> An attacker can cause a denial of service in Samba AD DC by triggering a null pointer dereference during LDAP search processing.

- **Severity:** Medium 6.5 (`CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Nov 2018
- **Updated:** 5 Aug 2024
- **Also known as:** ALPINE-CVE-2018-16851, DEBIAN-CVE-2018-16851, ECHO-c8c0-89cd-58d0, GHSA-48v5-hp4g-w2rv, UBUNTU-CVE-2018-16851

## What is CVE-2018-16851?

CVE-2018-16851 is a medium-severity vulnerability in Canonical Ubuntu Linux, published on 28 Nov 2018. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Samba from version 4.0.0 and before versions 4.7.12, 4.8.7, 4.9.3 is vulnerable to a denial of service. During the processing of an LDAP search before Samba's AD DC returns the LDAP entries to the client, the entries are cached in a single memory object with a maximum size of 256MB. When this size is reached, the Samba process providing the LDAP service will follow the NULL pointer, terminating the process. There is no further vulnerability associated with this issue, merely a denial of service.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2018-16851?

It affects 3 products.


Products: Canonical Ubuntu Linux, Debian Debian Linux, Samba Samba.

## How do I fix CVE-2018-16851?

Upgrade to a fixed version.

## Is CVE-2018-16851 being exploited?

There is no known exploitation of CVE-2018-16851 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-2018-16851 and fix it if it is affected.

What it is: CVE-2018-16851 is a medium-severity vulnerability in Canonical Ubuntu Linux, published on 28 Nov 2018. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2018-16851 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-2018-16851/ (Markdown: https://insights.sbomify.com/CVE-2018-16851/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-16851
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-16851
- OSV: https://osv.dev/vulnerability/CVE-2018-16851

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-16851/
Summaries are generated and may contain mistakes; the official description above is the record.