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NtpApplication

CVE-2023-26555

MEDIUM · 6.4 CVSS v3.1 Published 2023-04-11
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
69/100
Remediation priority · Elevated
No privileges Zero-click

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 · unedited
praecis_parse in ntpd/refclock_palisade.c in NTP 4.2.8p15 has an out-of-bounds write. Any attack method would be complex, e.g., with a manipulated GPS receiver.

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 · moderate confidence

An out-of-bounds write vulnerability exists in the praecis_parse function within ntpd/refclock_palisade.c in NTP version 4.2.8p15. The vulnerability stems from improper bounds checking when parsing reference clock data, allowing memory corruption. Exploitation requires a manipulated GPS receiver communicating with the NTP daemon, making the attack highly complex and requiring physical or logical access to the reference clock infrastructure.

MitigationUpgrade to a patched NTP version (4.2.8p16 or later). If upgrade is not immediately feasible, restrict network access to the refclock interface and ensure GPS receivers are on secured, monitored networks.

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
NtpApplication
Affected:= 4.2.8

CVSS 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
Physical
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:H/I:H/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 checks

Work through these to decide whether this CVE applies to you.

  1. Check installed NTP version
    Run 'ntpd --version' or check your package manager for ntp version (dpkg -l ntp, rpm -q ntp)
    Affected if Version is 4.2.8p15 or earlier (4.2.8 series before p16)
  2. Verify refclock_palisade support is compiled in
    Check if the ntpd binary includes refclock_palisade code: 'strings /path/to/ntpd | grep -i palisade' or 'ntpd -v 2>&1 | grep -i palisade'
    Affected if The palisade refclock driver is present in the binary
  3. Inspect ntp.conf for GPS or Palisade refclock configuration
    Look for 'server' or 'refclock' directives pointing to GPS, PALISADE, or generic NMEA drivers in /etc/ntp.conf or /etc/ntp/ntp.conf
    Affected if A refclock driver (especially GPS/PALISADE type) is configured
  4. Check for active refclock processes or modules
    Review running ntpd processes: 'ps aux | grep ntpd' and check for refclock-related logs in /var/log/ntp.log or /var/log/daemon.log
    Affected if NTP daemon is running with refclock support active

You are affected if running NTP 4.2.8p15 or earlier AND the palisade/GPS refclock driver is compiled in and actively configured or used.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to a patched NTP version (4.2.8p16 or later). If upgrade is not immediately feasible, restrict network access to the refclock interface and ensure GPS receivers are on secured, monitored networks.

Recommended fix High confidence

NTP 4.2.8p18 (or latest stable 4.2.8pX release)

  1. 1. Identify all systems running NTP daemon (ntpd) version 4.2.8 through 4.2.8p15
  2. 2. Obtain the latest stable NTP release from the official NTP distribution (ntp.org) or your Linux distribution's package repository
  3. 3. Stop the NTP daemon: sudo systemctl stop ntpd (or sudo service ntpd stop)
  4. 4. Install the updated NTP package (e.g., sudo apt-get update && sudo apt-get install ntp, or sudo yum update ntp, depending on your distribution)
  5. 5. Alternatively, download and compile NTP 4.2.8p18 or later from source: curl -s https://www.eecis.udel.edu/~ntp/ntp_spool/ntp4/ntp-4.2.8p18.tar.gz | tar xzf - && cd ntp-4.2.8p18 && ./configure --enable-clockchip --disable-parsim && make && sudo make install
  6. 6. Verify the installed version: ntpq -c version or ntpd --version
  7. 7. Start the NTP daemon: sudo systemctl start ntpd (or sudo service ntpd start)
  8. 8. Confirm NTP service is functioning correctly: ntpq -c peers
Caveat Minimal risk - standard point release upgrade. If compiling from source, ensure existing ntpd configuration (/etc/ntp.conf) is preserved and review any deprecated options. On some systems, consider switching to systemd-timesyncd or chrony as alternatives if NTP is being deprecated.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Ntp Scoped from the published advisory
  • Consultation4.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,480
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-26555 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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