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NtpApplication

CVE-2016-2517

MEDIUM · 5.3 CVSS v3.0 Published 2017-01-30
Fix available
A fix is available. Upgrade to after 4.2.8 or later.
See remediation →
59/100
Remediation priority · Elevated
Remotely reachable Zero-click

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 · unedited
NTP before 4.2.8p7 and 4.3.x before 4.3.92 allows remote attackers to cause a denial of service (prevent subsequent authentication) by leveraging knowledge of the controlkey or requestkey and sending a crafted packet to ntpd, which changes the value of trustedkey, controlkey, or requestkey. NOTE: this vulnerability exists because of a CVE-2016-2516 regression.

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 confidence

NTP daemon (ntpd) before 4.2.8p7 and 4.3.x before 4.3.92 allows remote attackers with knowledge of controlkey or requestkey to cause denial of service by sending crafted packets that modify trustedkey, controlkey, or requestkey values, preventing subsequent authentication. This is a regression from CVE-2016-2516.

MitigationUpgrade NTP to version 4.2.8p7/4.3.92 or later to patch the vulnerability; alternatively, restrict network access to ntpd and ensure strong key management to limit exposure.

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
NtpApplication
Affected:<= 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= 4.3.10

CVSS 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 checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed ntpd version
    Run 'ntpd --version' or 'ntpdc -V' or check your package manager for the ntp package version
    Affected if Version is 4.2.8 or lower, or is 4.3.0 through 4.3.10 (4.3.x before 4.3.92)
  2. Locate ntp.conf configuration file
    Common locations are /etc/ntp.conf or /etc/ntp/ntp.conf; check your system documentation for the default path
    Affected if File exists and contains ntpd configuration
  3. Check for enabled controlkey or requestkey
    Inspect ntp.conf for 'controlkey' or 'requestkey' directives - these enable authenticated management interface
    Affected if Either controlkey or requestkey is configured in ntp.conf (attacker needs knowledge of these keys to exploit)
  4. Verify network exposure of ntpd
    Check if ntpd is bound to network interfaces using 'netstat -anp | grep ntpd' or 'ss -anp | grep ntpd'
    Affected if ntpd is listening on accessible network interfaces (remote attackers need network access)

User is affected if ntpd version is 4.2.8 or lower, or any 4.3.x version before 4.3.92, AND ntpd is network-accessible AND controlkey or requestkey is configured in ntp.conf

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 data
Upgrade available Upgrade to a release after 4.2.8
Interim mitigation

Upgrade NTP to version 4.2.8p7/4.3.92 or later to patch the vulnerability; alternatively, restrict network access to ntpd and ensure strong key management to limit exposure.

Fix this in Ntp Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,800
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,880.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2016-2517 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
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