CVE-2018-8956
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 · uneditedntpd in ntp 4.2.8p10, 4.2.8p11, 4.2.8p12 and 4.2.8p13 allow remote attackers to prevent a broadcast client from synchronizing its clock with a broadcast NTP server via soofed mode 3 and mode 5 packets. The attacker must either be a part of the same broadcast network or control a slave in that broadcast network that can capture certain required packets on the attacker's behalf and send them to the attacker.
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 · moderate confidencentpd in NTP versions 4.2.8p10 through 4.2.8p12 contains a denial-of-service vulnerability in broadcast mode. A remote attacker on the same broadcast network segment (or controlling a node on that segment) can send spoofed mode 3 (client) and mode 5 (server) NTP packets to prevent broadcast clients from synchronizing their clocks with legitimate broadcast NTP servers.
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= 4.2.8CVSS 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
- Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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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Identify ntpd versionRun 'ntpd --version' or 'ntpdc -version' to obtain the installed NTP daemon versionAffected if Version is 4.2.8p10, 4.2.8p11, or 4.2.8p12 (the vulnerable series)
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Confirm broadcast mode is configuredInspect the NTP configuration file (typically /etc/ntp.conf or /etc/ntpd.conf) for 'broadcast' or 'multicast' directives, or run 'ntpq -c rv' to view runtime variables and look for broadcast client or server settingsAffected if Broadcast mode (broadcast or broadcastclient) directives are present and active in the configuration
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Verify network exposureCheck network interfaces and firewall rules to confirm the system is listening on NTP broadcast addresses (typically UDP port 123) or is configured to accept broadcast NTP packets on the local network segmentAffected if The system accepts NTP broadcast traffic on the local network without proper network-level access controls
A system is affected only if it runs ntpd version 4.2.8p10 through 4.2.8p12 AND has broadcast mode enabled, making it vulnerable to spoofed NTP packets on the broadcast network segment.
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 dataUpgrade to ntp version 4.2.8p13 or later. Additionally, implement network-level access controls on the broadcast domain to prevent unauthorized NTP packets.
- Consultation4.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,544.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2018-8956 — 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-2018-8956 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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- 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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