CVE-2015-1853: chrony before 1.31.1 does not properly protect state variables in authenticated symmetric NTP associations, wh

Q: How do I fix CVE-2015-1853?

chrony: upgrade to 1.31.1. Exact commands for each OS are on this page.

Q: Is CVE-2015-1853 being exploited?

CVE-2015-1853 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2015-1853 affect?

CVE-2015-1853 affects chrony. Severity is medium (CVSS 6.5). 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 times

Q: How urgent is CVE-2015-1853?

Priority 42/100. No elevated risk signals yet.

This month

MEDIUM 6.5UPGRADE

CVE-2015-1853 is a medium-severity flaw (CVSS 6.5) affecting chrony. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.7% (top 23%)
CISA exploited list	No
Published	2019-12-09
Last modified	2026-06-17

Publisher (CNA): Red Hat, Inc. · Vendor: tuxfamily

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2019-12-09 19:15 UTCPublished CVE record published
2026-06-17 00:23 UTCUpdated Record last modified

tuxfamily chrony UPGRADE

Affected: < 1.31.1

Fixed in: 1.31.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy chrony || rpm -q chrony || chrony --version

2. UPGRADE to 1.31.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade chrony

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade chrony

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2015-1853?

chrony: upgrade to 1.31.1. Exact commands for each OS are on this page.

Is CVE-2015-1853 being exploited?

CVE-2015-1853 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2015-1853 affect?

CVE-2015-1853 affects chrony. Severity is medium (CVSS 6.5). 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 times

How urgent is CVE-2015-1853?

Priority 42/100. No elevated risk signals yet.

Related CVEs

CVE-2020-14367 MEDIUM 6.0 UPGRADE MITIGATE A flaw was found in chrony versions before 3.5.1 when creating the PID file under the /var/run/chrony folder
CVE-2014-0021 HIGH 7.5 UPGRADE MITIGATE Chrony before 1.29.1 has traffic amplification in cmdmon protocol

References

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