# CVE-2018-16841: Use after free in samba

> An attacker with a valid certificate can cause a denial of service in Samba's KDC by triggering a double-free error during smart-card authentication.

- **Severity:** Medium 5.7 (`CVSS:3.0/AV:N/AC:L/PR:L/UI:R/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 28 Nov 2018
- **Updated:** 5 Aug 2024
- **Also known as:** ALPINE-CVE-2018-16841, DEBIAN-CVE-2018-16841, ECHO-3243-5f1a-98b7, GHSA-q3v8-mj9m-2wq4, UBUNTU-CVE-2018-16841

## What is CVE-2018-16841?

CVE-2018-16841 is a medium-severity use after free vulnerability in Canonical Ubuntu Linux, published on 28 Nov 2018. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

Samba from version 4.3.0 and before versions 4.7.12, 4.8.7 and 4.9.3 are vulnerable to a denial of service. When configured to accept smart-card authentication, Samba's KDC will call talloc_free() twice on the same memory if the principal in a validly signed certificate does not match the principal in the AS-REQ. This is only possible after authentication with a trusted certificate. talloc is robust against further corruption from a double-free with talloc_free() and directly calls abort(), terminating the KDC process.

Weakness: CWE-415 (Double Free), CWE-416 (Use After Free)

## Which versions are affected by CVE-2018-16841?

It affects 3 products.


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

## How do I fix CVE-2018-16841?

Apply the vendor's patch.

## Is CVE-2018-16841 being exploited?

There is no known exploitation of CVE-2018-16841 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-2018-16841 and fix it if it is affected.

What it is: CVE-2018-16841 is a medium-severity use after free vulnerability in Canonical Ubuntu Linux, published on 28 Nov 2018. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2018-16841 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-2018-16841/ (Markdown: https://insights.sbomify.com/CVE-2018-16841/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-16841
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-16841
- OSV: https://osv.dev/vulnerability/CVE-2018-16841

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-16841/
Summaries are generated and may contain mistakes; the official description above is the record.