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LinuxOperating system · Oracle

CVE-2015-7691

HIGH · 7.5 CVSS v3.1 Published 2017-08-07
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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
The crypto_xmit function in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to cause a denial of service (crash) via crafted packets containing particular autokey operations. NOTE: This vulnerability exists due to an incomplete fix for CVE-2014-9750.

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

The crypto_xmit function in ntpd contains a flaw in handling autokey operations. Remote attackers can send specially crafted packets with particular autokey operations that cause ntpd to crash, resulting in denial of service. This vulnerability is an incomplete fix for CVE-2014-9750, indicating the original patch did not fully address the underlying issue in the autokey protocol handling.

MitigationUpgrade NTP to version 4.2.8p4 or later, or 4.3.77 or later. If upgrading is not immediately feasible, consider disabling autokey authentication or restricting NTP access via firewall rules to limit exposure to untrusted 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
LinuxOperating system
Affected:= 6
Debian LinuxOperating system
Affected:= 7.0= 8.0= 9.0
Enterprise Linux DesktopOperating system
Affected:= 6.0= 7.0
Enterprise Linux ServerOperating system
Affected:= 6.0= 7.0
Enterprise Linux Server AusOperating system
Affected:= 7.3= 7.4= 7.6= 7.7
Enterprise Linux Server EusOperating system
Affected:= 7.3= 7.4= 7.5= 7.6= 7.7
Enterprise Linux Server TusOperating system
Affected:= 7.3= 7.6= 7.7
Enterprise Linux WorkstationOperating system
Affected:= 6.0= 7.0

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

CVSS:3.1/AV:N/AC:L/PR:N/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 checks

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

  1. Verify ntpd is installed
    Check if the NTP daemon is present on the system. On RHEL/CentOS/OEL use: rpm -q ntp. On Debian use: dpkg -l ntp. Alternatively, run: which ntpd
    Affected if ntpd is not installed on the system - this check is only applicable if NTP daemon is present
  2. Determine the installed NTP version
    Run: ntpd --version or ntpq -c version to obtain the exact version number of the NTP software
    Affected if The installed version is earlier than 4.2.8p4 or earlier than 4.3.77 (for 4.3.x branches) and matches one of the affected product versions listed in the CVE
  3. Check if autokey authentication is enabled
    Inspect the NTP configuration file (typically /etc/ntp.conf) for autokey-related directives such as 'crypto' or 'autokey', or check for the presence of keys or certificates in /etc/ntp/keys or /etc/ntp/ntpkey directory
    Affected if Autokey authentication is enabled - the vulnerability specifically affects systems using autokey operations; systems with autokey disabled are not vulnerable to this specific flaw
  4. Check for active NTP processes accepting network connections
    Run: netstat -anp | grep ntpd or ss -anp | grep ntpd to see if ntpd is listening on network ports, and verify if it accepts remote queries
    Affected if ntpd is running and listening on UDP port 123 (or configured to accept remote queries), exposing the service to network-based attacks

The system is affected if ntpd is installed with a version earlier than 4.2.8p4 (or earlier than 4.3.77), running on one of the affected Red Hat, Debian, or Oracle Linux versions listed, and autokey authentication is enabled with network exposure.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade NTP to version 4.2.8p4 or later, or 4.3.77 or later. If upgrading is not immediately feasible, consider disabling autokey authentication or restricting NTP access via firewall rules to limit exposure to untrusted networks.

Fix this in Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing4.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,360
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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-2015-7691 in production — separate from our analysis above.

No notes yet

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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
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  • Version or environment caveats, and links to real fixes
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