Debian LinuxOperating system · Debian
CVE-2015-7871
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 · uneditedCrypto-NAK packets in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to bypass authentication.
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 confidenceThe vulnerability allows remote attackers to bypass authentication in ntpd (Network Time Protocol daemon) through specially crafted 'crypto-NAK' packets. This enables an unauthenticated attacker to potentially manipulate time synchronization on affected systems by sending these malicious packets that circumvent the cryptographic authentication mechanism intended to verify NTP packet authenticity.
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
Debian LinuxOperating system
= 7.0= 8.0= 9.0>= 4.2.6, < 4.2.8>= 4.3.0, < 4.3.77= 4.2.5= 4.2.8all versionsall versionsall versionsall versionsall versionsCVSS 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
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/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 checksWork through these to decide whether this CVE applies to you.
-
Identify ntpd versionRun `ntpq -c version` or `ntpdc -c ver` to get the ntpd daemon version. On Debian-based systems, also run `dpkg -l | grep ntp` to check the installed package version.Affected if The version is 4.2.5, 4.2.8, or falls between 4.2.6 and 4.2.8p3, or between 4.3.0 and 4.3.76.
-
Check NTP authentication configurationInspect the ntpd configuration file at `/etc/ntp.conf` and look for authentication-related directives such as `trustedkey`, `requestkey`, `controlkey`, or `keys` directives.Affected if Authentication directives are present and configured, because the vulnerability specifically bypasses cryptographic authentication mechanisms.
-
Verify NTP is running and exposedCheck if ntpd is actively running using `ps aux | grep ntpd` and determine if the NTP service is listening on network interfaces (port 123/UDP). Use `netstat -anu | grep 123` or `ss -anu | grep 123`.Affected if ntpd is running and accessible over the network, as remote attackers need network access to send malicious crypto-NAK packets.
-
For NetApp products, check the underlying NTP implementationConsult NetApp product documentation or run system commands to determine the NTP version bundled with the affected NetApp products (Oncommand Balance, Performance Manager, Unified Manager, Clustered Data Ontap, Data Ontap).Affected if The NTP implementation version matches the vulnerable ntpd version ranges.
A system is affected if it runs a vulnerable ntpd version (4.2.5, 4.2.8, 4.2.6-4.2.8p3, or 4.3.0-4.3.76) with NTP authentication configured and network exposure to untrusted sources.
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.
dbcve · scoped4.2.84.3.77
Apply the ntpd security update to version 4.2.8p4/4.3.77 or later to patch the authentication bypass. Additionally, restrict NTP traffic to trusted sources using firewall rules or access control lists to limit exposure until patching is complete.
NTP 4.2.8p4 or later (4.2.x branch), or NTP 4.3.77 or later (4.3.x branch)
- Identify the current installed NTP version using 'ntpd --version' or 'dpkg -l | grep ntp'
- For Debian systems: Run 'apt-get update' followed by 'apt-get install ntp' to install the latest available package
- For NTP from source: Download ntp-4.2.8p4 or later from ntp.org (e.g., 'wget http://archive.ntp.org/ntp4/ntp-4.2.8p4.tar.gz')
- Extract and compile the source: './configure --prefix=/usr --enable-linuxcaps', 'make', 'make install'
- Restart the ntpd service after upgrade using 'service ntpd restart' or 'systemctl restart ntpd'
- Verify the fixed version is running: 'ntpd --version' should show 4.2.8p4 or later, or 4.3.77 or later
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Debian Linux
Scoped from the published advisory
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,408.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2015-7871 — 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-2015-7871 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data