CVE-2015-1853
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedchrony 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidencechrony before 1.31.1 fails to properly protect internal state variables in authenticated symmetric NTP associations. An attacker with knowledge of the NTP peering relationship (the IP addresses of both NTP peers) can send crafted NTP packets containing random timestamps, causing the chrony daemon to become unable to synchronize time, resulting in a denial of service.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 1.31.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Determine installed chrony versionRun 'chronyd --version' or check your package manager (e.g., 'dpkg -l chrony', 'rpm -qi chrony')Affected if The version displayed is lower than 1.31.1
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Identify if chrony is configured as an NTP peerExamine chrony configuration files (typically /etc/chrony/chrony.conf or /etc/chronyd.conf) for 'peer' directives; also check 'chronyc peers' outputAffected if The configuration contains 'peer' directives pointing to other NTP servers, indicating symmetric peer associations
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Confirm NTP authentication is in useReview chrony configuration for 'key' or 'authhash' directives that configure NTP authentication between peersAffected if Authenticated symmetric associations are configured (the vulnerability specifically affects authenticated NTP peering)
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Assess network exposure of NTP serviceCheck if UDP port 123 is accessible from untrusted networks (run 'netstat -ulnp | grep 123' or check firewall rules)Affected if Port 123/UDP is exposed to network segments where attackers could spoof the peer IP address
A system is affected if it runs chrony version below 1.31.1 with authenticated symmetric NTP peer associations and has accessible NTP ports, allowing an attacker with knowledge of the peer IPs to send crafted packets causing synchronization failure.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data1.31.1
Upgrade chrony to version 1.31.1 or later. If immediate upgrading is not feasible, restrict network access to NTP ports (123/UDP) so only trusted peers can communicate, or temporarily disable NTP authentication if acceptable for the environment.
- Consultation1.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2015-1853 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2015-1853 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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