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Debian LinuxOperating system · Debian

CVE-2016-2774

MEDIUM · 5.9 CVSS v3.1 Published 2016-03-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
68/100
Remediation priority · Elevated
High EPSS 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
ISC DHCP 4.1.x before 4.1-ESV-R13 and 4.2.x and 4.3.x before 4.3.4 does not restrict the number of concurrent TCP sessions, which allows remote attackers to cause a denial of service (INSIST assertion failure or request-processing outage) by establishing many sessions.

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

ISC DHCP server versions 4.1.x before 4.1-ESV-R13, 4.2.x, and 4.3.x before 4.3.4 lack restrictions on concurrent TCP sessions, allowing remote attackers to exhaust server resources by establishing many simultaneous connections. This triggers INSIST assertion failures or request-processing outages, causing denial of service.

MitigationUpgrade to ISC DHCP 4.1-ESV-R13 or 4.3.4 or later to patch the vulnerability. Alternatively, implement network-level rate limiting or firewall rules to restrict concurrent TCP connections to the DHCP server.

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
Affected:= 8.0
Ubuntu LinuxOperating system
Affected:= 14.04= 16.04= 17.10
DhcpApplication
Affected:= 4.1-esv= 4.1.0= 4.1.1= 4.1.2= 4.2.0= 4.2.1= 4.2.2= 4.2.3= 4.2.4= 4.2.5= 4.2.6= 4.2.7

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
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:H/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. Identify ISC DHCP server installation
    Run 'dpkg -l | grep isc-dhcp-server' on Debian/Ubuntu, or 'rpm -qa | grep dhcp' on Red Hat systems to check if the ISC DHCP server package is installed.
    Affected if The package is installed and running as a DHCP server.
  2. Determine installed DHCP server version
    Run 'dpkg -l isc-dhcp-server' or check the output of 'dhcpd -v' or 'dhcpd --version' to obtain the exact version number.
    Affected if The version is 4.1.x before 4.1-ESV-R13, any 4.2.x, or 4.3.x before 4.3.4.
  3. Verify DHCP server is accepting TCP connections
    Check the DHCP server configuration file (typically /etc/dhcp/dhcpd.conf) and confirm the server is listening. Also verify the service is active by running 'systemctl status isc-dhcp-server' or 'service dhcpd status'.
    Affected if The DHCP server is running and accepting connections on port 67/UDP and/or 67/TCP.
  4. Monitor active TCP connections to DHCP port
    Run 'ss -tulpn | grep :67' or 'netstat -tulpn | grep :67' to observe current TCP connections. Use 'ss -tulpn' repeatedly to detect a spike in simultaneous connections.
    Affected if Many concurrent TCP connections are observed or the server becomes unresponsive under connection load.
  5. Check OS distribution and version
    Run 'cat /etc/os-release' to identify the Linux distribution. For Debian 8.0, Ubuntu 14.04, 16.04, or 17.10, the packaged ISC DHCP versions are affected.
    Affected if Running Debian 8.0 or Ubuntu 14.04/16.04/17.10 with the default ISC DHCP package.

You are affected if the ISC DHCP server is running and its version falls within 4.1.x before 4.1-ESV-R13, any 4.2.x, or 4.3.x before 4.3.4, and the server accepts TCP connections which can be exhausted by an attacker.

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 to ISC DHCP 4.1-ESV-R13 or 4.3.4 or later to patch the vulnerability. Alternatively, implement network-level rate limiting or firewall rules to restrict concurrent TCP connections to the DHCP server.

Fix this in Debian Linux Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,120
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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-2016-2774 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
  • 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