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Ubuntu LinuxOperating system · Canonical

CVE-2016-7426

HIGH · 7.5 CVSS v3.1 Published 2017-01-13
Fix available
A fix is available. Upgrade to 4.2.8 / 4.3.94 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges 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 4.2.8p9 rate limits responses received from the configured sources when rate limiting for all associations is enabled, which allows remote attackers to cause a denial of service (prevent responses from the sources) by sending responses with a spoofed source address.

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

In NTP versions before 4.2.8p9, rate limiting when enabled for all associations incorrectly applies to responses received from legitimately configured sources. An attacker can exploit this by spoofing the source address of NTP responses, causing the server to rate-limit and block legitimate time sources, resulting in a denial of service.

MitigationUpgrade NTP to version 4.2.8p9 or later, which contains the fix for this rate-limiting logic flaw. If immediate patching is not possible, review NTP association configurations and monitor for anomalous rate-limiting behavior.

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
Ubuntu LinuxOperating system
Affected:= 12.04
Enterprise Linux DesktopOperating system
Affected:= 6.0= 7.0
Enterprise Linux ServerOperating system
Affected:= 6.0= 7.0
Enterprise Linux Server AusOperating system
Affected:= 7.3= 7.4= 7.6= 7.7
Enterprise Linux Server EusOperating system
Affected:= 7.3= 7.4= 7.5= 7.6= 7.7
Enterprise Linux Server TusOperating system
Affected:= 7.3= 7.6= 7.7
Enterprise Linux WorkstationOperating system
Affected:= 6.0= 7.0
NtpApplication
Affected:>= 4.2.6, < 4.2.8>= 4.3.0, < 4.3.94= 4.2.5= 4.2.8

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
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/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. Check NTP daemon version
    Run 'ntpd --version' or 'ntpdc -version' to determine the installed NTP version
    Affected if Version is before 4.2.8p9 and falls within the affected ranges: 4.2.5, 4.2.6 through 4.2.7, 4.2.8, 4.3.0 through 4.3.93
  2. Verify rate limiting is enabled
    Inspect /etc/ntp.conf or /etc/ntp/ntp.conf for 'restrict ... limited' directives, or run 'ntpdc -c reslist' to see active restrict lines
    Affected if Rate limiting with 'limited' modifier is configured, especially without specifying a kiss code (e.g., 'kod' or 'ignore')
  3. Check for configured NTP associations
    Run 'ntpdc -c peers' or 'ntpq -c peers' to list configured time sources
    Affected if One or more remote NTP servers are configured as associations, as these can be blocked by rate limiting when the flaw triggers
  4. Identify OS and version
    Check /etc/lsb-release for Ubuntu or 'cat /etc/redhat-release' for RHEL
    Affected if Running Ubuntu 12.04, RHEL 6.0, RHEL 7.0, or RHEL 7.3-7.7 variants as listed in affected products

Your environment is affected if NTP version is before 4.2.8p9, rate limiting is enabled with the 'limited' directive, and you have configured remote NTP associations that could be blocked by the flawed rate-limiting logic.

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 4.2.8 / 4.3.94 or later
Fixed in 4.2.84.3.94
Interim mitigation

Upgrade NTP to version 4.2.8p9 or later, which contains the fix for this rate-limiting logic flaw. If immediate patching is not possible, review NTP association configurations and monitor for anomalous rate-limiting behavior.

Fix this in Ubuntu Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,390
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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-2016-7426 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
  • No spam, self-promotion, credentials, or personal data