Description
ntp_request.c in ntpd in NTP before 4.2.4p8, and 4.2.5, allows remote attackers to cause a denial of service (CPU and bandwidth consumption) by using MODE_PRIVATE to send a spoofed (1) request or (2) response packet that triggers a continuous exchange of MODE_PRIVATE error responses between two NTP daemons.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 11 | ntp | 1:4.2.4p8+dfsg-1 | — |
| Debian 5.0 | ntp | 1:4.2.4p4+dfsg-8lenny3 | DSA-1948-1 |
| Debian 4.0 | ntp | 1:4.2.2.p4+dfsg-2etch4 | DSA-1948-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 5 | ntp | 4.2.2p1-9.el5_4.1 | RHSA-2009:1648 |
| RHEL 4 | ntp | 4.2.0.a.20040617-8.el4_8.1 | RHSA-2009:1648 |
| RHEL 3 | ntp | 4.1.2-6.el3 | RHSA-2009:1651 |
Public exploits
Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.
Metasploit 1 module
-
NTP.org ntpd Reserved Mode Denial of Service
auxiliary/dos/ntp/ntpd_reserved_dos
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Advisories 6
- RHSA-2009:1651 Red Hat Security Advisory: ntp security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- RHSA-2009:1648 Red Hat Security Advisory: ntp security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- DSA-1948-1 ntp - denial of service Debian Security (DSA / DLA) · Mar 9, 2026
- WID-SEC-2024-0672 UDP-basierte Protokollimplementierungen: Mehrere Schwachstellen ermöglichen Denial of Service BSI CERT-Bund (WID) · Mar 19, 2024
- WID-SEC-2023-1747 Moxa Switch: Schwachstelle ermöglicht Denial of Service BSI CERT-Bund (WID) · Jul 13, 2023
- VDE-2022-032 AUMA: Multiple Vulnerabilities in Automation Runtime NTP Service CERT@VDE · Aug 9, 2022
References
- VU#568372 third-party-advisory
- 38832 third-party-advisory
- http://kb.juniper.net/InfoCenter/index?page=content&id=JSA10673
- oval:org.mitre.oval:def:11225 vdb-entry signature
- http://support.avaya.com/css/P8/documents/100071808
- 38794 third-party-advisory
- [security-announce] 20100303 VMSA-2010-0004 ESX Service Console and vMA third party updates mailing-list
- FEDORA-2009-13121 vendor-advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=531213
- 38764 third-party-advisory
- http://support.ntp.org/bin/view/Main/SecurityNotice#DoS_attack_from_certain_NTP_mode
- http://www.kb.cert.org/vuls/id/MAPG-7X7V6J
- oval:org.mitre.oval:def:19376 vdb-entry signature
- 37255 vdb-entry
- SSRT101144 vendor-advisory
- 39593 third-party-advisory
- IZ71047 vendor-advisory
- ADV-2010-0993 vdb-entry
- DSA-1948 vendor-advisory
- http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=560074
- http://aix.software.ibm.com/aix/efixes/security/xntpd_advisory.asc
- HPSBUX02639 vendor-advisory
- 1021781 vendor-advisory
- IZ68659 vendor-advisory
- https://support.ntp.org/bugs/show_bug.cgi?id=1331
- oval:org.mitre.oval:def:7076 vdb-entry signature
- 37922 third-party-advisory
- 38834 third-party-advisory
- FEDORA-2009-13090 vendor-advisory
- http://security-tracker.debian.org/tracker/CVE-2009-3563
- 1023298 vdb-entry
- oval:org.mitre.oval:def:12141 vdb-entry signature
- RHSA-2009:1651 vendor-advisory
- 37629 third-party-advisory
- RHSA-2010:0095 vendor-advisory
- http://kb.juniper.net/InfoCenter/index?page=content&id=JSA10691
- [announce] 20091208 NTP 4.2.4p8 Released mailing-list
- ADV-2010-0510 vdb-entry
- RHSA-2009:1648 vendor-advisory
- http://www.kb.cert.org/vuls/id/MAPG-7X7VD7
- ADV-2010-0528 vdb-entry
- VU#417980 third-party-advisory