PatchTheCVECVE-2016-5117: OpenNTPD before 6.0p1 does not validate the CN for HTTPS constraint requests, which allows remote attackers to
CVE-2016-5117 is a medium-severity flaw (CVSS 5.9) affecting openntpd. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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.
Why this priority
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Risk facts
| CVSS score | 5.9 (Medium) |
| Attack vector | Network (remote) |
| Attack complexity | High |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 0.7% (top 47%) |
| CISA exploited list | No |
| Weakness | CWE-254 |
| Published | 2017-01-31 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2016-5117?
openntpd: upgrade to newer than 6.0. Exact commands for each OS are on this page.
Is CVE-2016-5117 being exploited?
CVE-2016-5117 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2016-5117 affect?
CVE-2016-5117 affects openntpd. Severity is medium (CVSS 5.9). 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.
How urgent is CVE-2016-5117?
Priority 39/100. Remotely exploitable, no login, no user action