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PatchSiren cyber security CVE debrief

CVE-2015-8138 Ntp CVE debrief

This NTP flaw lets a remote attacker bypass origin timestamp validation by sending a packet with the origin timestamp set to zero. The supplied NVD record rates the issue as medium severity with limited integrity impact, but because it is network-reachable and requires no privileges or user interaction, exposed ntpd deployments should be reviewed and patched.

Vendor
Ntp
Product
Unknown
CVSS
MEDIUM 5.3
CISA KEV
Not listed in stored evidence
Original CVE published
2021-04-13
Original CVE updated
2025-06-10
Advisory published
2021-04-13
Advisory updated
2025-06-10

Who should care

Operators of systems running NTP/ntpd, especially internet-exposed servers, appliances, and embedded products that rely on accurate time synchronization.

Technical summary

The supplied NVD record describes a validation weakness in NTP's handling of origin timestamps. A packet with the origin timestamp field set to zero can bypass the intended origin timestamp check. NVD lists affected releases as NTP before 4.2.8p6 and 4.3.x before 4.3.90, and maps the issue to CWE-20. The supplied CVSS vector is CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

Defensive priority

Medium priority: the CVSS score is modest, but the flaw is remotely reachable and can affect time-trust logic. Prioritize exposed or mission-critical time services and any systems where clock integrity matters.

Recommended defensive actions

  • Identify all hosts and appliances running ntpd or vendor-packaged NTP derived from the affected releases.
  • Upgrade to a fixed NTP release at or beyond the vendor-remediated versions referenced by the NVD record.
  • Validate that downstream distributions and appliance firmware have incorporated the fix, since the reference list shows broad vendor packaging and advisory coverage.
  • Restrict exposure of NTP services to trusted networks where possible and monitor for unexpected NTP traffic patterns.
  • After remediation, verify time synchronization behavior and alerting on critical systems that depend on precise timestamps.

Evidence notes

Evidence comes from the supplied NVD record, which states the zero-origin-timestamp bypass, the affected version ranges, and the CVSS vector CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N. The reference list also includes the NTP vendor security notice and multiple downstream advisories, showing the issue was publicly tracked and remediated across distributions.

Sources and references

Verified primary and authoritative sources

  • CVE-2015-8138 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2015-8138

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2015-8138 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2015-8138

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.