CVE-2016-2516
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedNTP before 4.2.8p7 and 4.3.x before 4.3.92, when mode7 is enabled, allows remote attackers to cause a denial of service (ntpd abort) by using the same IP address multiple times in an unconfig directive.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceNTP daemon (ntpd) before versions 4.2.8p7 and 4.3.92 contains a denial of service vulnerability when mode7 (a debug/control mode) is enabled. Remote attackers can cause ntpd to abort by sending packets with the same IP address multiple times in an unconfig directive.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data<= 4.2.8= 4.3.0= 4.3.1= 4.3.2= 4.3.3= 4.3.4= 4.3.5= 4.3.6= 4.3.7= 4.3.8= 4.3.9= 4.3.10CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.0/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Determine installed ntpd versionRun `ntpd --version` or `ntpdc -v` to get the exact version number. On Linux, also check the package version with `rpm -q ntp` or `dpkg -l ntp`.Affected if Version is 4.2.8 or lower, or any version from 4.3.0 through 4.3.10 inclusive.
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Locate ntpd configuration fileThe primary configuration is typically at /etc/ntp.conf or /etc/ntp/ntp.conf. Check the ntpd man page or running process for any alternate locations.Affected if Configuration file exists and is in use by the ntpd service.
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Check if mode7 is explicitly disabledOpen the ntp.conf file and search for a line containing `disable mode7`. This directive must be present to protect against the vulnerability.Affected if The `disable mode7` directive is NOT present in the configuration file.
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Verify mode7 is not enabled at runtimeRun `ntpq -c rv` or `ntpdc -c sysinfo` to inspect runtime variables. Look for a mode7 variable. Alternatively, check if ntpd is listening on port 123/UDP which may indicate mode7 activity.Affected if mode7 is not disabled and the service is running with mode7 potentially accessible.
You are affected if your ntpd version falls within 4.3.0-4.3.10 or is 4.2.8 or earlier AND the `disable mode7` directive is absent from your ntp.conf file.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataDisable mode7 in ntpd configuration by adding 'disable mode7' to ntp.conf, or upgrade to NTP version 4.2.8p7/4.3.92 or later which addresses this issue.
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2016-2516 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2016-2516 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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