CVE-2020-13817Network attack vector

Daemon exit or clock change via predictable timestamps

Published Jun 4, 2020 · Updated May 5, 2025

Denial of service in NTP ntpd before 4.2.8p14 and 4.3.x before 4.3.100 allows remote attackers to alter time or exit the daemon. Predictable transmit timestamps let spoofed replies pass origin-timestamp checks when presented as upstream IPv4 server traffic. Exploitation requires an off-path attacker who can query the instance and flood spoofed packets while it uses unauthenticated IPv4 sources; eight consecutive successes can shift the clock or terminate ntpd.

CVSS severity5.9
Medium
EPSS probability3.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in NTP ntpd before 4.2.8p14 and 4.3.x before 4.3.100 allows remote attackers to alter time or exit the daemon. Predictable transmit timestamps let spoofed replies pass origin-timestamp checks when presented as upstream IPv4 server traffic. Exploitation requires an off-path attacker who can query the instance and flood spoofed packets while it uses unauthenticated IPv4 sources; eight consecutive successes can shift the clock or terminate ntpd.

The record

CVE
CVE-2020-13817
Published
Jun 4, 2020
Updated
May 5, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-330, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 4, 2020CVE publishedPublication date reported by the CVE source.
  2. May 5, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.4NTP ProjectAV:N/AC:H/Au:N/C:N/I:N/A:C
5.8NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:P
7.4NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
7.4CISA-ADPCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:H
5.9NTP ProjectCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-330Use of Insufficiently Random Values
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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