What is CVE-2023-26553?

CVE-2023-26553 is a medium-severity vulnerability in NTP, classified under Out-of-bounds Write. CVSS score: 5.6/10. Published 2023-04-11.

How severe is CVE-2023-26553?

Medium severity. CVSS v3 base score is 5.6 out of 10.

Buffer overflow in NTP

CVE-2023-26553

mstolfp in libntp/mstolfp.c in NTP 4.2.8p15 has an out-of-bounds write when copying the trailing number. An adversary may be able to attack a client ntpq process, but cannot attack ntpd.

Vulnerability class: Buffer Overflow

Published 2023-04-11 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.6 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L.

EPSS exploit prediction

EPSS: 0.007 (51.1th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 51st percentile — 51.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: -0.000

Affected products

NTP — versions 4.2.8

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

github.com/spwpun/ntp-4.2.8p15-cves/blob/main/CVE-2023-26553 (Third Party Advisory)
github.com/spwpun/ntp-4.2.8p15-cves/issues/1 (Third Party Advisory)

Frequently asked questions

What is CVE-2023-26553?: CVE-2023-26553 is a medium-severity vulnerability in NTP, classified under Out-of-bounds Write. CVSS score: 5.6/10. Published 2023-04-11.
How severe is CVE-2023-26553?: Medium severity. CVSS v3 base score is 5.6 out of 10.