ntp: Using port 123 for modes where a fixed port number is not required facilitates off-path attacks.
Published Apr 18, 2019
8.1
HIGHCVSS 3.0
EPSS 2.64%
Description
Network Time Protocol (NTP), as specified in RFC 5905, uses port 123 even for modes where a fixed port number is not required, which makes it easier for remote attackers to conduct off-path attacks.
Affected products
No data.
No data.
Red Hat Enterprise Linux 5
ntp
Will not fix
Red Hat Enterprise Linux 6
ntp
Will not fix
Red Hat Enterprise Linux 7
ntp
Will not fix
| Product | Package | State | Advisory |
|---|---|---|---|
| Red Hat Enterprise Linux 5 | ntp | Will not fix | n/a |
| Red Hat Enterprise Linux 6 | ntp | Will not fix | n/a |
| Red Hat Enterprise Linux 7 | ntp | Will not fix | n/a |
No package ranges for this CVE.
Remediation
Red Hat mitigation
On Red Hat Enterprise Linux 6 and later, switching from ntp to chrony is recommended. Among other design improvements, chrony uses a randomised source port by default. If using ntp, the source port can be randomised by iptables masquerading rules, effectively mitigating this vulnerability: iptables -t nat -I POSTROUTING -p udp -m udp --sport 123 -j MASQUERADE --to-ports 60000-61000
Metrics
No CVSS v4.0 score for this CVE.
No CVSS v3.1 score for this CVE.
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
AV:N/AC:M/Au:N/C:P/I:P/A:P
This CVE is not in the KEV list.
No CISA SSVC assessment for this CVE yet.
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.
Score over time
2021–2026- EPSS v1
- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Percentile over time
- EPSS v1
- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Table of values (18 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 1, 2026 | 2.64% (0.02637) | 85.02th | v5 (v2026.06.15) |
| Jun 15, 2026 | 2.64% (0.02637) | 83.53th | v5 (v2026.06.15) |
| Jun 19, 2025 | 1.38% (0.01383) | 79.41th | v4 (v2025.03.14) |
| Mar 30, 2025 | 2.90% (0.02898) | 85.11th | v4 (v2025.03.14) |
| Mar 29, 2025 | 5.62% (0.05618) | 83.48th | v4 (v2025.03.14) |
| Mar 19, 2025 | 2.90% (0.02898) | 84.80th | v4 (v2025.03.14) |
| Jul 20, 2024 | 1.40% (0.01396) | 86.55th | v3 (v2023.03.01) |
| Apr 11, 2024 | 1.40% (0.01396) | 86.17th | v3 (v2023.03.01) |
| Mar 27, 2024 | 0.98% (0.00980) | 83.09th | v3 (v2023.03.01) |
| Mar 7, 2023 | 0.97% (0.00972) | 81.03th | v3 (v2023.03.01) |
| Mar 6, 2023 | 1.21% (0.01213) | 66.61th | v2 (v2022.01.01) |
| Feb 17, 2023 | 1.21% (0.01213) | 66.22th | v2 (v2022.01.01) |
| Apr 1, 2022 | 1.21% (0.01213) | 64.21th | v2 (v2022.01.01) |
| Feb 4, 2022 | 15.35% (0.15351) | 91.59th | v2 (v2022.01.01) |
| Feb 3, 2022 | 5.60% (0.05603) | 80.32th | v1 |
| Jan 6, 2022 | 5.60% (0.05603) | 80.12th | v1 |
| Sep 1, 2021 | 1.31% (0.01306) | 69.61th | v1 |
| Apr 14, 2021 | 1.31% (0.01306) | 0.00th | v1 |
References (8)
- http://www.securityfocus.com/bid/108010 vdb-entryx_refsource_BIDThird Party Advisory
- https://access.redhat.com/security/cve/CVE-2019-11331 Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=1703341 Issue Tracking
- https://nvd.nist.gov/vuln/detail/CVE-2019-11331
- https://support.f5.com/csp/article/K09940637 x_refsource_CONFIRM
- https://support.f5.com/csp/article/K09940637?utm_source=f5support&%3Butm_medium=RSS x_refsource_CONFIRM
- https://tools.ietf.org/html/draft-gont-ntp-port-randomization-00 x_refsource_MISCThird Party Advisory
- https://www.cve.org/CVERecord?id=CVE-2019-11331
| Link | Providers | Tags |
|---|---|---|
| http://www.securityfocus.com/bid/108010 | vdb-entryx_refsource_BIDThird Party Advisory | |
| https://access.redhat.com/security/cve/CVE-2019-11331 | Vendor Advisory | |
| https://bugzilla.redhat.com/show_bug.cgi?id=1703341 | Issue Tracking | |
| https://nvd.nist.gov/vuln/detail/CVE-2019-11331 | ||
| https://support.f5.com/csp/article/K09940637 | x_refsource_CONFIRM | |
| https://support.f5.com/csp/article/K09940637?utm_source=f5support&%3Butm_medium=RSS | x_refsource_CONFIRM | |
| https://tools.ietf.org/html/draft-gont-ntp-port-randomization-00 | x_refsource_MISCThird Party Advisory | |
| https://www.cve.org/CVERecord?id=CVE-2019-11331 |
Change history (0)
No recorded changes yet.