What is CVE-2015-1853?

CVE-2015-1853 is a medium-severity vulnerability in Chrony. CVSS score: 6.5/10. Published 2019-12-09.

How severe is CVE-2015-1853?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Chrony

CVE-2015-1853

chrony before 1.31.1 does not properly protect state variables in authenticated symmetric NTP associations, which allows remote attackers with knowledge of NTP peering to cause a denial of service (inability to synchronize) via random timestamps in crafted NTP data packets.

Published 2019-12-09 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.017 (76.2th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 76th percentile — 76.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.017 · newest: 0.017 · change: 0.000

Affected products

Chrony — versions before 1.31.1
Tuxfamily Chrony

References

security.gentoo.org/glsa/201507-01 (Third Party Advisory)
chrony.tuxfamily.org/News.html (Release Notes, Vendor Advisory)

Frequently asked questions

What is CVE-2015-1853?: CVE-2015-1853 is a medium-severity vulnerability in Chrony. CVSS score: 6.5/10. Published 2019-12-09.
How severe is CVE-2015-1853?: Medium severity. CVSS v3 base score is 6.5 out of 10.