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Fencer Intel
medium 6.5

CVE-2015-1853 json

chrony before 1.31.1 does not properly protect state variables in authenticated symmetric NTP associations, which allows remote attackers w…

published 2019-12-09 6 y ago modified 2026-06-17 4 mo ago also EUVD-2015-1962

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.7%
EPSS 1.7% chance of exploitation in 30 days, percentile 77%
public exploits
0
none known

Summary

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.

Patch / fix

  • tuxfamily chrony 1.31.1
  • chrony Debian 14, Debian 13, Debian 12 1.30-2

debian advisories DEBIAN-CVE-2015-1853

  • chrony Ubuntu 14.04 LTS 1.29-1ubuntu0.1

ubuntu advisories UBUNTU-CVE-2015-1853

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • chrony RHEL 7 2.1.1-1.el7

red hat advisories RHSA-2015:2241

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2015-1853 updated cvss 4.3

chrony: authentication doesn't protect symmetric associations against DoS attacks

  • Red Hat Enterprise Linux Client (v. 7) chrony 2.1.1-1.el7 Red Hat Enterprise Linux ComputeNode (v. 7) chrony 2.1.1-1.el7 Red Hat Enterprise Linux Server (v. 7) chrony 2.1.1-1.el7 Red Hat Enterprise Linux Workstation (v. 7) chrony 2.1.1-1.el7
    fixed: vendor fix RHSA-2015:2241

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.70% chance of exploitation in the next 30 days, higher than 77% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:N/A:P

Affected products

  • chrony chrony

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.