CVE-2015-7871 [Critical] | Authentication Bypass in Ntp

CVE-2015-7871 is rated High Risk (77.9/100): CVSS Critical severity, with high exploitation likelihood (EPSS 83.58%, 99th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +3.96% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize remediation.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-21	79.62%	83.58%	+3.96%
2	2025-12-28	76.65%	79.62%	+2.97%
3	2025-12-27	—	76.65%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-21

79.62%

83.58%

+3.96%

2025-12-28

76.65%

79.62%

+2.97%

2025-12-27

—

76.65%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
9.8	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H` 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:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. 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:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	5.9	[email protected]
7.5	2.0	HIGH	`AV:N/AC:L/Au:N/C:P/I:P/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	10.0	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

9.8

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H 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:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
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:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

5.9

[email protected]

7.5

2.0

HIGH

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

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

10.0

6.4

[email protected]

OS Trackers for CVE-2015-7871

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2015-7871 not yet assigned priority: Debian including 1 source packages (ntp), 1 status rows across 1 suites (bullseye): resolved 1.	https://security-tracker.debian.org/tracker/CVE-2015-7871
`gentoo`	normal	CVE-2015-7871: 2 GLSA(s) (201604-03, 201607-15), 5 atom(s) (app-emulation/pvgrub, app-emulation/xen, app-emulation/xen-pvgrub, app-emulation/xen-tools, net-misc/ntp); latest impact normal.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2015-7871
`redhat`	high	—	https://access.redhat.com/security/cve/CVE-2015-7871
`ubuntu`	medium	CVE-2015-7871 medium priority: Ubuntu including 1 source packages (ntp), 5 status rows across 5 suites (precise, trusty, upstream, vivid, wily): released 4, needs-triage 1.	https://ubuntu.com/security/CVE-2015-7871

Affected software / configurations for CVE-2015-7871

Vendor	Product	Version	Raw CPE
ntp	ntp	>= 4.2.6, < 4.2.8	cpe:2.3:a:ntp:ntp::::::::
ntp	ntp	>= 4.3.0, < 4.3.77	cpe:2.3:a:ntp:ntp::::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p186::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p187::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p188::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p189::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p190::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p191::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p192::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p193::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p194::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p195::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p196::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p197::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p198::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p199::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p200::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p201::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p202::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p203::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p204::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p205::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p206::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p207::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p208::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p209::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p210::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p211::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p212::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p213::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p214::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p215::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p216::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p217::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p218::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p219::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p220::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p221::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p222::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p223::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p224::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p225::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p226::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p227::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p228::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p229::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p230::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p231_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p232_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p233_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p234_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p235_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p236_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p237_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p238_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p239_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p240_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p241_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p242_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p243_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p244_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p245_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p246_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p247_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p248_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p249_rc1::::::
ntp	ntp	4.2.5	cpe:2.3:a:ntp:ntp:4.2.5:p250_rc1::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p1::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p1-beta1::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p1-beta2::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p1-beta3::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p1-beta4::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p1-beta5::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p1-rc1::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p1-rc2::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p2::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p2-rc1::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p2-rc2::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p2-rc3::::::
ntp	ntp	4.2.8	cpe:2.3:a:ntp:ntp:4.2.8:p3::::::

References for CVE-2015-7871

URL	Tags
http://support.ntp.org/bin/view/Main/NtpBug2941	Vendor Advisory
http://www.debian.org/security/2015/dsa-3388	Third Party Advisory
http://www.securityfocus.com/bid/77287	Third Party Advisory VDB Entry
http://www.securitytracker.com/id/1033951	Third Party Advisory VDB Entry
https://bugzilla.redhat.com/show_bug.cgi?id=1274265	Issue Tracking Third Party Advisory VDB Entry
https://cert-portal.siemens.com/productcert/pdf/ssa-497656.pdf
https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05270839	Third Party Advisory VDB Entry
https://security.gentoo.org/glsa/201604-03	Third Party Advisory VDB Entry
https://security.gentoo.org/glsa/201607-15	Third Party Advisory VDB Entry
https://security.netapp.com/advisory/ntap-20171004-0001/	Third Party Advisory

URL

CVE-2015-7871

Exploit prediction scoring system (EPSS) score for CVE-2015-7871

Common vulnerability scoring system (CVSS) metrics for CVE-2015-7871

Weakness enumeration for CVE-2015-7871

OS Trackers for CVE-2015-7871

Affected software / configurations for CVE-2015-7871

References for CVE-2015-7871