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NtpApplication

CVE-2023-26551

MEDIUM · 5.6 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 →
65/100
Remediation priority · Elevated
Remotely reachable 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
mstolfp in libntp/mstolfp.c in NTP 4.2.8p15 has an out-of-bounds write in the cp<cpdec while loop. An adversary may be able to attack a client ntpq process, but cannot attack ntpd.

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 confidence

An out-of-bounds write vulnerability exists in the mstolfp function in libntp/mstolfp.c in NTP version 4.2.8p15. The vulnerability occurs in a while loop where the cp pointer is compared against cpdec, allowing writes beyond buffer boundaries. This affects the ntpq client utility but not the ntpd daemon.

MitigationUpgrade to NTP version 4.2.8p16 or later which contains the fix for this vulnerability. If immediate patching is not possible, restrict access to ntpq and avoid processing untrusted time data.

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
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L

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 if ntpq utility is installed
    Run 'which ntpq' or 'dpkg -l | grep ntp' (Debian) / 'rpm -qa | grep ntp' (RHEL) to see if the ntpq binary exists on the system
    Affected if ntpq is installed and its version is 4.2.8p1 through 4.2.8p15
  2. Identify the exact NTP version
    Run 'ntpq --version' or 'ntpq -c version' to obtain the precise version number of the installed ntpq utility
    Affected if Version shows 4.2.8p15 or earlier (4.2.8p1 through 4.2.8p15 are affected)
  3. Confirm the vulnerable component
    The flaw is in the mstolfp function within libntp/mstolfp.c used by ntpq. Verify ntpq is present: run 'ntpq -c help' to confirm the utility executes
    Affected if ntpq executes successfully and is based on the vulnerable libntp code (versions 4.2.8p1-p15)
  4. Verify this is not the patched version
    Check version output for 'p16' or later. The fix was released in version 4.2.8p16. Compare your version string against the affected range
    Affected if Version shows 4.2.8p15 or lower (versions prior to the p16 patch)

You are affected if the ntpq utility is installed and its version is 4.2.8p15 or any earlier p-release (p1-p15), since the out-of-bounds write vulnerability exists in the mstolfp function of those specific versions.

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 NTP version 4.2.8p16 or later which contains the fix for this vulnerability. If immediate patching is not possible, restrict access to ntpq and avoid processing untrusted time data.

Recommended fix Moderate confidence

NTP 4.2.8p16 or later stable release (check ntp.org for latest)

  1. 1. Identify the current NTP version installed: `ntpd --version` or `ntpq --version`
  2. 2. Download the latest stable NTP release from the official NTP download page (ntp.org) or your distribution's package repository
  3. 3. If using a Linux distribution, update via package manager: `apt-get update && apt-get upgrade ntp` (Debian/Ubuntu) or `yum update ntp` (RHEL/CentOS)
  4. 4. Verify the new version includes the fix for CVE-2023-26551
  5. 5. Restart any running ntpq or ntpd processes if necessary
Caveat Ensure any custom NTP configuration is compatible with the new version before production deployment

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

Fix this in Ntp Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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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-2023-26551 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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