No exploitation reportedFix available

CVE-2015-7871

Q: Is CVE-2015-7871 actively exploited?

Active exploitation of CVE-2015-7871 has not been confirmed. Its EPSS score was 81.8% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2015-7871?

CVE-2015-7871 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

No exploitation reported by the sources we read.

Published2017-08-07
Fixed in4.3.77 · 4.2.8
WeaknessCWE-287

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Crypto-NAK packets in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to bypass authentication.

Timeline

dates in UTC

2017-08-0720:29CVE publishedNVD
2026-10-2319:23EPSS crossed 10 %FIRST EPSS

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2015-7871?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2015-7871?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Ntp

Branch	Affected	Fixed in	Source
4.3	≥ 4.3.0, < 4.3.77	4.3.77	NVD
4.2	≥ 4.2.6, < 4.2.8	4.2.8	NVD
4.2	= 4.2.5	no fix published	NVD
4.2	= 4.2.8	no fix published	NVD

Debian debian linux

Branch	Affected	Fixed in	Source
7.0	= 7.0	no fix published	NVD
8.0	= 8.0	no fix published	NVD
9.0	= 9.0	no fix published	NVD

Netapp clustered data ontap

Branch	Affected	Fixed in	Source
—	all versions	no fix published	NVD

4 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

ICSA-21-103-11 CISA4 known affected
Siemens TIM 4R-IE Devices
SIPLUS NET TIM 4R-IE (6AG1800-4BA00-7AA0) · SIPLUS NET TIM 4R-IE DNP3 (6AG1803-4BA00-7AA0) · TIM 4R-IE (6NH7800-4BA00) · +1 more
ICSA-15-356-01 CISA2 known affected
Siemens RUGGEDCOM ROX-based Devices NTP Vulnerabilities
Siemens RUGGEDCOM ROX I: vers:all/* · Siemens ROX II: <2.9.0

Full record on NVD

Fix

Update Ntp to 4.3.77 · 4.2.8
Workaround from the vendor CISA ICSA-21-103-11 · 4 productsDeactivate NTP-based time syncronization of the device, if enabled. The feature is disabled by default.
Workaround from the vendor CISA ICSA-21-103-11 · 4 productsConfigure an additional firewall to prevent communication to the port udp/123 of an affected device.
Mitigation from the vendor CISA ICSA-15-356-01 · 2 productsUpdate to the latest version. (http://www.siemens.com/automation/support-request)
No fix planned, says the vendor CISA ICSA-21-103-11 · 4 productsCurrently no fix is planned

Advisories and patches

support.ntp.orgVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.19.8read 2026-10-23
NVDCVSS 2.07.5read 2026-10-23
NVDweakness (CWE)CWE-287read 2026-10-23
FIRST EPSSEPSS score81.8 %read 2026-10-23

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published: 2017-08-07
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2015-7871?

Crypto-NAK packets in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to bypass authentication.

Is CVE-2015-7871 actively exploited?

Active exploitation of CVE-2015-7871 has not been confirmed. Its EPSS score was 81.8% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2015-7871?

CVE-2015-7871 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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