# CVE-2016-5117: Security feature bypass in n/a

> OpenNTPD fails to validate certificate common names, allowing attackers to bypass man-in-the-middle protections for timestamp constraints.

- **Severity:** Medium 5.9 (`CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Jan 2017
- **Updated:** 6 Aug 2024
- **Also known as:** DEBIAN-CVE-2016-5117, GHSA-4m25-49gx-cpq6

## What is CVE-2016-5117?

CVE-2016-5117 is a medium-severity vulnerability in n/a, published on 31 Jan 2017. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

OpenNTPD before 6.0p1 does not validate the CN for HTTPS constraint requests, which allows remote attackers to bypass the man-in-the-middle mitigations via a crafted timestamp constraint with a valid certificate.

Weakness: CWE-254

## Which versions are affected by CVE-2016-5117?

It affects 1 product.


Products: Openntpd Openntpd.

## How do I fix CVE-2016-5117?

Upgrade to a fixed version.

## Is CVE-2016-5117 being exploited?

There is no known exploitation of CVE-2016-5117 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2016-5117 and fix it if it is affected.

What it is: CVE-2016-5117 is a medium-severity vulnerability in n/a, published on 31 Jan 2017. 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-2016-5117 in the wild and no public exploit code.

Affected product: n/a. 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-2016-5117/ (Markdown: https://insights.sbomify.com/CVE-2016-5117/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2016-5117
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2016-5117
- OSV: https://osv.dev/vulnerability/CVE-2016-5117

---
From sbomify Insights: https://insights.sbomify.com/CVE-2016-5117/
Summaries are generated and may contain mistakes; the official description above is the record.