CRITICAL
ntp: crypto-NAK symmetric association authentication bypass vulnerability
Published Aug 7, 2017
9.8
CRITICALCVSS 3.1
EPSS 81.76%
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.
Affected products
No data.
Configuration 1
OR
- ≥ 4.2.6 · < 4.2.8
- ≥ 4.3.0 · < 4.3.77
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.5
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
- 4.2.8
Configuration 2
OR
- 7.0
- 8.0
- 9.0
Configuration 3
OR
- n/a
- n/a
- n/a
- n/a
- n/a
No data.
Red Hat Enterprise Linux 5
ntp
Not affected
Red Hat Enterprise Linux 6
ntp
Not affected
Red Hat Enterprise Linux 7
ntp
Not affected
| Product | Package | State | Advisory |
|---|---|---|---|
| Red Hat Enterprise Linux 5 | ntp | Not affected | n/a |
| Red Hat Enterprise Linux 6 | ntp | Not affected | n/a |
| Red Hat Enterprise Linux 7 | ntp | Not affected | n/a |
No package ranges for this CVE.
Remediation
Red Hat statement
This issue did not affect the versions of ntp as shipped with Red Hat Enterprise Linux 5, 6, and 7.
Metrics
No CVSS v4.0 score for this CVE.
9.8 CRITICAL NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality Impact High
Integrity Impact High
Availability Impact High
No CVSS v3.0 score for this CVE.
7.5 HIGH NVD
AV:N/AC:L/Au:N/C:P/I:P/A:P
Access Vector Network
Access Complexity Low
Authentication None
Confidentiality Impact Partial
Integrity Impact Partial
Availability Impact Partial
This CVE is not in the KEV list.
No CISA SSVC assessment for this CVE yet.
81.76% 0.81762
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.
EPSS probability 0.81762
Score over time
2022–2026- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Percentile over time
- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Table of values (21 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 1, 2026 | 81.76% (0.81762) | 99.64th | v5 (v2026.06.15) |
| Jun 15, 2026 | 81.76% (0.81762) | 99.60th | v5 (v2026.06.15) |
| May 21, 2026 | 83.58% (0.83579) | 99.30th | v4 (v2025.03.14) |
| Dec 28, 2025 | 79.62% (0.79620) | 99.05th | v4 (v2025.03.14) |
| Dec 27, 2025 | 76.65% (0.76653) | 98.90th | v4 (v2025.03.14) |
| Dec 15, 2025 | 79.62% (0.79620) | 99.04th | v4 (v2025.03.14) |
| Dec 13, 2025 | 80.78% (0.80776) | 99.10th | v4 (v2025.03.14) |
| Aug 10, 2025 | 76.65% (0.76653) | 98.89th | v4 (v2025.03.14) |
| Mar 30, 2025 | 84.00% (0.84001) | 99.25th | v4 (v2025.03.14) |
| Mar 29, 2025 | 86.02% (0.86020) | 99.24th | v4 (v2025.03.14) |
| Mar 17, 2025 | 83.21% (0.83207) | 99.22th | v4 (v2025.03.14) |
| Dec 12, 2024 | 97.01% (0.97007) | 99.80th | v3 (v2023.03.01) |
| Mar 10, 2024 | 97.02% (0.97024) | 99.73th | v3 (v2023.03.01) |
| Feb 1, 2024 | 97.00% (0.97004) | 99.69th | v3 (v2023.03.01) |
| Nov 11, 2023 | 96.97% (0.96975) | 99.66th | v3 (v2023.03.01) |
| Oct 3, 2023 | 97.10% (0.97101) | 99.69th | v3 (v2023.03.01) |
| Aug 23, 2023 | 97.13% (0.97129) | 99.68th | v3 (v2023.03.01) |
| Jul 18, 2023 | 97.10% (0.97099) | 99.66th | v3 (v2023.03.01) |
| Mar 7, 2023 | 97.06% (0.97064) | 99.56th | v3 (v2023.03.01) |
| Mar 6, 2023 | 60.02% (0.60019) | 98.91th | v2 (v2022.01.01) |
| Feb 4, 2022 | 60.02% (0.60019) | 98.62th | v2 (v2022.01.01) |
Weaknesses (2)
References (15)
- http://support.ntp.org/bin/view/Main/NtpBug2941 x_refsource_CONFIRMVendor Advisory
- http://support.ntp.org/bin/view/Main/SecurityNotice#October_2015_NTP_Security_Vulner
- http://talosintel.com/reports/TALOS-2015-0069/
- http://www.debian.org/security/2015/dsa-3388 vendor-advisoryx_refsource_DEBIANThird Party Advisory
- http://www.securityfocus.com/bid/77287 vdb-entryx_refsource_BIDThird Party AdvisoryVDB Entry
- http://www.securitytracker.com/id/1033951 vdb-entryx_refsource_SECTRACKThird Party AdvisoryVDB Entry
- https://access.redhat.com/security/cve/CVE-2015-7871 Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=1274265 x_refsource_CONFIRMIssue TrackingThird Party AdvisoryVDB Entry
- https://cert-portal.siemens.com/productcert/pdf/ssa-497656.pdf x_refsource_CONFIRM
- https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05270839 x_refsource_CONFIRMThird Party AdvisoryVDB Entry
- https://nvd.nist.gov/vuln/detail/CVE-2015-7871
- https://security.gentoo.org/glsa/201604-03 vendor-advisoryx_refsource_GENTOOThird Party AdvisoryVDB Entry
- https://security.gentoo.org/glsa/201607-15 vendor-advisoryx_refsource_GENTOOThird Party AdvisoryVDB Entry
- https://security.netapp.com/advisory/ntap-20171004-0001/ x_refsource_CONFIRMThird Party Advisory
- https://www.cve.org/CVERecord?id=CVE-2015-7871
Change history (0)
No recorded changes yet.
Sources
CVE.org / MITRE
Status PUBLISHED
Assigner mitre
Published Aug 7, 2017
Updated Aug 6, 2024
Reserved Oct 19, 2015
Link CVE-2015-7871
CISA Vulnrichment
Updated n/a