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Vulnerability record · CVE-2016-7434 · published 13 January 2017

CVE-2016-7434: NTP read_mru_list input validation flaw causes remote crash

Ntp · Ntp

The read_mru_list function in NTP before 4.2.8p9 fails to properly validate crafted mrulist queries, allowing a remote attacker to crash the daemon. Because NTP is widely deployed for time synchronization, a crash can disrupt time services across many hosts.

7.5 CVSS 3.1 High EPSS 53% · top 1.1% CWE-20 · Improper input validation
7.5CVSS 3.1 base score, v2 4.3
53%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
20References, 2 tagged exploit
17 Jun 2026Last modified by NVD

Description

The read_mru_list function in NTP before 4.2.8p9 allows remote attackers to cause a denial of service (crash) via a crafted mrulist query.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 20 September 2026. Confidence: high.

high priorityRemote unauthenticated crash with a public exploit and very high EPSS, though no KEV listing and impact limited to denial of service.

What it is

The read_mru_list function in NTP before 4.2.8p9 fails to properly validate crafted mrulist queries, allowing a remote attacker to crash the daemon. Because NTP is widely deployed for time synchronization, a crash can disrupt time services across many hosts.

Impact

An unauthenticated remote attacker can cause a denial of service by crashing the NTP daemon; there is no confidentiality or integrity impact per the CVSS vector.

Attack surface

Reachable over the network via a crafted mrulist query to the NTP service; the CVSS vector shows no privileges or user interaction required.

Exploitation

Not listed in CISA KEV, but EPSS is high (0.529, ~98.9th percentile) and a public Exploit-DB entry (40806) exists, indicating practical exploitability.

What to do

  • Upgrade NTP to 4.2.8p9 or later, or apply the vendor patch for your distribution.
  • On HPE HP-UX, apply the referenced HPE security bulletin update for hpux-ntp.
  • Restrict NTP query access to trusted networks and disable or block mrulist queries where not needed.
  • Monitor vendor advisories (NTP, FreeBSD, HPE) for backported fixes and apply them promptly.

Detection

  • Monitor NTP daemon logs for crashes, restarts, or abnormal termination correlated with incoming mrulist queries.
  • Detect anomalous or malformed mrulist query patterns to NTP ports (UDP 123) using network monitoring or IDS signatures.
  • Track NTP process uptime and alert on unexpected restarts on servers running pre-4.2.8p9 versions.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://nwtime.org/ntp428p9_release/ Third Party Advisory
http://support.ntp.org/bin/view/Main/NtpBug3082 Issue TrackingMitigationVendor Advisory
http://support.ntp.org/bin/view/Main/SecurityNotice#Recent_Vulnerabilities Release NotesVendor Advisory
http://www.securityfocus.com/bid/94448 Third Party AdvisoryVDB Entry
http://www.securitytracker.com/id/1037354 Third Party AdvisoryVDB Entry
https://bto.bluecoat.com/security-advisory/sa139 Third Party Advisory
https://h20566.www2.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03706en_us Third Party Advisory
https://security.FreeBSD.org/advisories/FreeBSD-SA-16:39.ntp.asc Third Party Advisory
https://www.exploit-db.com/exploits/40806/ ExploitThird Party AdvisoryVDB Entry
https://www.kb.cert.org/vuls/id/633847 Third Party AdvisoryUS Government Resource
http://nwtime.org/ntp428p9_release/ Third Party Advisory
http://support.ntp.org/bin/view/Main/NtpBug3082 Issue TrackingMitigationVendor Advisory
http://support.ntp.org/bin/view/Main/SecurityNotice#Recent_Vulnerabilities Release NotesVendor Advisory
http://www.securityfocus.com/bid/94448 Third Party AdvisoryVDB Entry
http://www.securitytracker.com/id/1037354 Third Party AdvisoryVDB Entry
https://bto.bluecoat.com/security-advisory/sa139 Third Party Advisory
https://h20566.www2.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03706en_us Third Party Advisory
https://security.FreeBSD.org/advisories/FreeBSD-SA-16:39.ntp.asc Third Party Advisory
https://www.exploit-db.com/exploits/40806/ ExploitThird Party AdvisoryVDB Entry
https://www.kb.cert.org/vuls/id/633847 Third Party AdvisoryUS Government Resource

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2016-7434), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.