How severe is CVE-2016-2517?

CVE-2016-2517 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2016-2517 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 9% (95th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-2517?

CVE-2016-2517 primarily affects Ntp. In total, 93 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-2517?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2016-2517 published?

CVE-2016-2517 was published on 2017-01-30 and last updated on 2026-06-17.

CVE-2016-2517

CVE-2016-2517 is a medium-severity vulnerability in Ntp with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v2: 4.9
EPSS exploit prediction: 9% (95th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Ntp
Published: 2017-01-30
Last modified: 2026-06-17

Description

NTP before 4.2.8p7 and 4.3.x before 4.3.92 allows remote attackers to cause a denial of service (prevent subsequent authentication) by leveraging knowledge of the controlkey or requestkey and sending a crafted packet to ntpd, which changes the value of trustedkey, controlkey, or requestkey. NOTE: this vulnerability exists because of a CVE-2016-2516 regression.

Frequently asked questions

What is CVE-2016-2517?: NTP before 4.2.8p7 and 4.3.x before 4.3.92 allows remote attackers to cause a denial of service (prevent subsequent authentication) by leveraging knowledge of the controlkey or requestkey and sending a crafted packet to ntpd, which changes the value of trustedkey, controlkey, or requestkey. NOTE: this vulnerability exists because of a CVE-2016-2516 regression.
How severe is CVE-2016-2517?: CVE-2016-2517 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with high attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2016-2517 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 9% (95th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-2517?: CVE-2016-2517 primarily affects Ntp. In total, 93 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2016-2517?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2016-2517 published?: CVE-2016-2517 was published on 2017-01-30 and last updated on 2026-06-17.

References

Affected products (93)

cpe:2.3:a:ntp:ntp:*:p6:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.0:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.1:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.2:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.3:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.4:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.5:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.6:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.7:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.8:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.9:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.10:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.11:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.12:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.13:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.14:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.15:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.16:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.17:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.18:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.19:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.20:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.21:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.22:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.23:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.24:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.25:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.26:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.27:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.28:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.29:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.30:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.31:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.32:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.33:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.34:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.35:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.36:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.37:*:*:*:*:*:*:*
cpe:2.3:a:ntp:ntp:4.3.38:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

197.248.207.139 (ipv4-addr)
135.129.128.247 (ipv4-addr)
119.201.59.224 (ipv4-addr)
125.212.244.35 (ipv4-addr)
202.29.220.126 (ipv4-addr)
93.42.227.251 (ipv4-addr)
82.209.191.11 (ipv4-addr)
119.204.60.250 (ipv4-addr)