CVE-2016-1551 [Low] | Security Vulnerability in Ntp

ntpd in NTP 4.2.8p3 and NTPsec a5fb34b9cc89b92a8fef2f459004865c93bb7f92 relies on the underlying operating system to protect it from requests that impersonate reference clocks. Because reference clocks are treated like other peers and stored in the same structure, any packet with a source ip address of a reference clock (127.127.1.1 for example) that reaches the receive() function will match that reference clock's peer record and will be treated as a trusted peer. Any system that lacks the typical martian packet filtering which would block these packets is in danger of having its time controlled by an attacker.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-12-28	0.73%	0.98%	+0.24%
2	2025-12-27	0.98%	0.73%	-0.24%
3	2025-12-20	—	0.98%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-12-28

0.73%

0.98%

+0.24%

2025-12-27

0.98%

0.73%

-0.24%

2025-12-20

—

0.98%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
3.7	3.0	LOW	`CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:N) Service keeps running; no real outage angle.	2.2	1.4	[email protected]
2.6	2.0	LOW	`AV:N/AC:H/Au:N/C:N/I:P/A:N` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:H) Exploitation requires uncommon or highly specific conditions. Authentication (AU:N) No authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:N) No availability impact.	4.9	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

3.7

3.0

LOW

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N): Service keeps running; no real outage angle.

2.2

1.4

[email protected]

2.6

2.0

LOW

AV:N/AC:H/Au:N/C:N/I:P/A:N Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:H): Exploitation requires uncommon or highly specific conditions.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:N): No availability impact.

4.9

2.9

[email protected]

OS Trackers for CVE-2016-1551

vendor	priority	summary	link
`debian`	unimportant	CVE-2016-1551 unimportant priority: Debian including 1 source packages (ntp), 1 status rows across 1 suites (bullseye): resolved 1.	https://security-tracker.debian.org/tracker/CVE-2016-1551
`gentoo`	normal	CVE-2016-1551: 1 GLSA(s) (201607-15), 1 atom(s) (net-misc/ntp); latest impact normal.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2016-1551
`redhat`	low	—	https://access.redhat.com/security/cve/CVE-2016-1551
`suse`	low	CVE-2016-1551 severity low: SUSE including 22 source package names (ntp-4.2.8p10-63.3, ntp-4.2.8p11-2.12, …), 80 product×package rows across 54 product lines (Image SLES12-SP5-Azure-BYOS, Image SLES12-SP5-Azure-Basic-On-Demand, … (54 product lines)): Fixed 80.	https://www.suse.com/security/cve/CVE-2016-1551/
`ubuntu`	negligible	CVE-2016-1551 negligible priority: Ubuntu including 1 source packages (ntp), 5 status rows across 5 suites (precise, trusty, upstream, wily, xenial): not-affected 4, released 1.	https://ubuntu.com/security/CVE-2016-1551

Affected software / configurations for CVE-2016-1551

Vendor	Product	Version	Raw CPE
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p3::::::
ntpsec	ntpsec	a5fb34b9cc89b92a8fef2f459004865c93bb7f92	cpe:2.3:a:ntpsec:ntpsec:a5fb34b9cc89b92a8fef2f459004865c93bb7f92:::::::*

References for CVE-2016-1551

URL	Tags
http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html	Third Party Advisory
http://www.securityfocus.com/bid/88219	Third Party Advisory VDB Entry
http://www.securitytracker.com/id/1035705
http://www.talosintelligence.com/reports/TALOS-2016-0132/	Third Party Advisory
https://security.FreeBSD.org/advisories/FreeBSD-SA-16:16.ntp.asc
https://security.gentoo.org/glsa/201607-15
https://security.netapp.com/advisory/ntap-20171004-0002/

URL

CVE-2016-1551

Exploit prediction scoring system (EPSS) score for CVE-2016-1551

Common vulnerability scoring system (CVSS) metrics for CVE-2016-1551

Weakness enumeration for CVE-2016-1551

OS Trackers for CVE-2016-1551

Affected software / configurations for CVE-2016-1551

References for CVE-2016-1551