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.
Conclusion & alert: CVE-2009-3563 is rated Moderate Risk (61.8/100): CVSS Medium severity, with high exploitation likelihood (EPSS 81.11%, 99th percentile). Core evidence: EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +1.48% over the last day, indicating growing attacker interest. Mandatory action: High exploitation likelihood—assess exposure and prioritize remediation.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2026-05-01 | 79.63% | 81.11% | +1.48% |
| 2 | 2026-03-28 | 79.91% | 79.63% | -0.28% |
| 3 | 2026-03-21 | — | 79.91% | — |
Full EPSS history (31 records total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 6.4 | 2.0 | MEDIUM |
|
10.0 | 4.9 | [email protected] |
| vendor | priority | summary | link |
|---|---|---|---|
debian
|
medium | CVE-2009-3563 medium priority: Debian including 1 source packages (ntp), 1 status rows across 1 suites (bullseye): resolved 1. | https://security-tracker.debian.org/tracker/CVE-2009-3563 |
gentoo
|
normal | CVE-2009-3563: 1 GLSA(s) (201001-01), 1 atom(s) (net-misc/ntp); latest impact normal. | https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2009-3563 |
redhat
|
medium | — | https://access.redhat.com/security/cve/CVE-2009-3563 |
ubuntu
|
medium | CVE-2009-3563 medium priority: Ubuntu including 1 source packages (ntp), 6 status rows across 6 suites (dapper, hardy, intrepid, jaunty, karmic, upstream): released 6. | https://ubuntu.com/security/CVE-2009-3563 |
| Vendor | Product | Version | Raw CPE |
|---|---|---|---|
| ntp | ntp | <= 4.2.2p4 | cpe:2.3:a:ntp:ntp:*:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.72 | cpe:2.3:a:ntp:ntp:4.0.72:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.73 | cpe:2.3:a:ntp:ntp:4.0.73:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.90 | cpe:2.3:a:ntp:ntp:4.0.90:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.91 | cpe:2.3:a:ntp:ntp:4.0.91:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.92 | cpe:2.3:a:ntp:ntp:4.0.92:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.93 | cpe:2.3:a:ntp:ntp:4.0.93:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.94 | cpe:2.3:a:ntp:ntp:4.0.94:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.95 | cpe:2.3:a:ntp:ntp:4.0.95:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.96 | cpe:2.3:a:ntp:ntp:4.0.96:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.97 | cpe:2.3:a:ntp:ntp:4.0.97:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.98 | cpe:2.3:a:ntp:ntp:4.0.98:*:*:*:*:*:*:* |
| ntp | ntp | 4.0.99 | cpe:2.3:a:ntp:ntp:4.0.99:*:*:*:*:*:*:* |
| ntp | ntp | 4.1.0 | cpe:2.3:a:ntp:ntp:4.1.0:*:*:*:*:*:*:* |
| ntp | ntp | 4.1.2 | cpe:2.3:a:ntp:ntp:4.1.2:*:*:*:*:*:*:* |
| ntp | ntp | 4.2.0 | cpe:2.3:a:ntp:ntp:4.2.0:*:*:*:*:*:*:* |
| ntp | ntp | 4.2.2 | cpe:2.3:a:ntp:ntp:4.2.2:*:*:*:*:*:*:* |
| ntp | ntp | 4.2.2p1 | cpe:2.3:a:ntp:ntp:4.2.2p1:*:*:*:*:*:*:* |
| ntp | ntp | 4.2.2p2 | cpe:2.3:a:ntp:ntp:4.2.2p2:*:*:*:*:*:*:* |
| ntp | ntp | 4.2.2p3 | cpe:2.3:a:ntp:ntp:4.2.2p3:*:*:*:*:*:*:* |
| ntp | ntp | 4.2.5 | cpe:2.3:a:ntp:ntp:4.2.5:*:*:*:*:*:*:* |