CVE-2018-5733· NVD / CVE Program· CNA isc

A malicious client can overflow a reference counter in ISC dhcpd

A malicious client which is allowed to send very large amounts of traffic (billions of packets) to a DHCP server can eventually overflow a 32-bit reference counter, potentially causing dhcpd to crash. Affects ISC DHCP 4.1.0 -> 4.1-ESV-R15, 4.2.0 -> 4.2.8, 4.3.0 -> 4.3.6, 4.4.0.

HighCVSS 7.5 · v3.1—No exploit Fix available

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Published: Jan 16, 2019
Updated: Jun 16, 2026
EPSS: 20.2% · 97th percentile
CWE: CWE-190

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Action score

Monitor

Low priority for now.

CVSS: 30 / 40 · 7.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 6 / 30 · 20.2%

CNA vs NVD score

NVD: 7.5
CNA · isc: 5.9; 1.6 point gap

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Affected systems

Vendor	Product	CPE
isc	dhcp	cpe:2.3:a:isc:dhcp
redhat	enterprise linux desktop	cpe:2.3:o:redhat:enterprise_linux_desktop
redhat	enterprise linux server	cpe:2.3:o:redhat:enterprise_linux_server
redhat	enterprise linux server aus	cpe:2.3:o:redhat:enterprise_linux_server_aus
redhat	enterprise linux server eus	cpe:2.3:o:redhat:enterprise_linux_server_eus
redhat	enterprise linux workstation	cpe:2.3:o:redhat:enterprise_linux_workstation
canonical	ubuntu linux	cpe:2.3:o:canonical:ubuntu_linux
debian	debian linux	cpe:2.3:o:debian:debian_linux

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

canonical ubuntu linux14.04
canonical ubuntu linux16.04
canonical ubuntu linux17.10
debian debian linux7.0
debian debian linux8.0
debian debian linux9.0
isc dhcp4.2.0 and later · up to 4.2.8 inclusive
isc dhcp4.3.0 and later · up to 4.3.6 inclusive
isc dhcp4.1-esv
isc dhcp4.1.0
isc dhcp4.4.0
redhat enterprise linux desktop6.0
redhat enterprise linux desktop7.0
redhat enterprise linux server6.0
redhat enterprise linux server7.0
redhat enterprise linux server aus7.4
redhat enterprise linux server aus7.6
redhat enterprise linux server eus7.4
redhat enterprise linux server eus7.5
redhat enterprise linux server eus7.6

Versions reported by the vendor

Affected version ranges reported by the assigning authority (isc). Independent of NVD's CPE analysis and usually ahead of it.

ISC ISC DHCP
- ISC DHCP 4.1.0 -> 4.1-ESV-R15, 4.2.0 -> 4.2.8, 4.3.0 -> 4.3.6, 4.4.0affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Alpine:v3.10	dhcp	from 4.2.0 · before 4.4.1-r0	4.4.1-r0
Debian:12	isc-dhcp	before 4.3.5-3.1	4.3.5-3.1
Debian:7	isc-dhcp	before 4.2.2.dfsg.1-5+deb70u9	4.2.2.dfsg.1-5+deb70u9
Debian:8	isc-dhcp	before 4.3.1-6+deb8u3	4.3.1-6+deb8u3
Debian:9	isc-dhcp	before 4.3.5-3+deb9u1	4.3.5-3+deb9u1
openSUSE:Tumbleweed	dhcp	before 4.4.2.P1-2.4	4.4.2.P1-2.4
Red Hat:enterprise_linux:6::client	dhclient	before 12:4.1.1-53.P1.el6_9.3	12:4.1.1-53.P1.el6_9.3
Red Hat:enterprise_linux:6::client	dhcp	before 12:4.1.1-53.P1.el6_9.3	12:4.1.1-53.P1.el6_9.3
Red Hat:enterprise_linux:6::client	dhcp-common	before 12:4.1.1-53.P1.el6_9.3	12:4.1.1-53.P1.el6_9.3
Red Hat:enterprise_linux:6::client	dhcp-debuginfo	before 12:4.1.1-53.P1.el6_9.3	12:4.1.1-53.P1.el6_9.3
Red Hat:enterprise_linux:6::client	dhcp-devel	before 12:4.1.1-53.P1.el6_9.3	12:4.1.1-53.P1.el6_9.3
Red Hat:enterprise_linux:7::client	dhclient	before 12:4.2.5-58.el7_4.3	12:4.2.5-58.el7_4.3
Red Hat:enterprise_linux:7::client	dhcp	before 12:4.2.5-58.el7_4.3	12:4.2.5-58.el7_4.3
Red Hat:enterprise_linux:7::client	dhcp-common	before 12:4.2.5-58.el7_4.3	12:4.2.5-58.el7_4.3
Red Hat:enterprise_linux:7::client	dhcp-debuginfo	before 12:4.2.5-58.el7_4.3	12:4.2.5-58.el7_4.3
Red Hat:enterprise_linux:7::client	dhcp-devel	before 12:4.2.5-58.el7_4.3	12:4.2.5-58.el7_4.3
Red Hat:enterprise_linux:7::client	dhcp-libs	before 12:4.2.5-58.el7_4.3	12:4.2.5-58.el7_4.3
SUSE:Linux Enterprise Desktop 12 SP2	dhcp	before 4.3.3-10.14.1	4.3.3-10.14.1
SUSE:Linux Enterprise Software Development Kit 11 SP4	dhcp	before 4.2.4.P2-0.28.8.1	4.2.4.P2-0.28.8.1

Same product

isc: all records

Other highest-scoring records for the same primary product.

CVE-2011-0997dhclient in ISC DHCP 3.0.x through 4.2.x before 4.2.1-P1, 3.1-ESV before 3.1-ESV-R1, and 4.1-ESV before 4.1-ESV-R2 allows remote attackers t
55Plan
CVE-2017-3144Failure to properly clean up closed OMAPI connections can exhaust available sockets
52Plan
CVE-2015-8605ISC DHCP 4.x before 4.1-ESV-R12-P1, 4.2.x, and 4.3.x before 4.3.3-P1 allows remote attackers to cause a denial of service (application crash
51Plan
CVE-2009-0692Stack-based buffer overflow in the script_write_params method in client/dhclient.c in ISC DHCP dhclient 4.1 before 4.1.0p1, 4.0 before 4.0.1
48Plan
CVE-2016-2774ISC 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 rem
45Plan
CVE-2011-2749The server in ISC DHCP 3.x and 4.x before 4.2.2, 3.1-ESV before 3.1-ESV-R3, and 4.1-ESV before 4.1-ESV-R3 allows remote attackers to cause a
43Plan

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
alpine:dhcp	4.4.1-r0 · Alpine:v3.10	Package registry (OSV)
debian:isc-dhcp	4.3.5-3.1 · Debian:12	Package registry (OSV)
opensuse:dhcp	4.4.2.P1-2.4 · openSUSE:Tumbleweed	Package registry (OSV)
red hat:dhclient	12:4.1.1-53.P1.el6_9.3 · Red Hat:enterprise_linux:6::client	Package registry (OSV)
red hat:dhcp	12:4.1.1-53.P1.el6_9.3 · Red Hat:enterprise_linux:6::client	Package registry (OSV)
red hat:dhcp-common	12:4.1.1-53.P1.el6_9.3 · Red Hat:enterprise_linux:6::client	Package registry (OSV)
red hat:dhcp-debuginfo	12:4.1.1-53.P1.el6_9.3 · Red Hat:enterprise_linux:6::client	Package registry (OSV)
red hat:dhcp-devel	12:4.1.1-53.P1.el6_9.3 · Red Hat:enterprise_linux:6::client	Package registry (OSV)
red hat:dhcp-libs	12:4.2.5-58.el7_4.3 · Red Hat:enterprise_linux:7::client	Package registry (OSV)
suse:dhcp	4.2.4.P2-0.28.8.1 · SUSE:Linux Enterprise Software Development Kit 11 SP4	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Felix Wilhelm, Google Security Team

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-190 · Integer Overflow or Wraparound

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

Forced Integer OverflowCAPEC-92likelihood: High · High

ATT&CK techniques

—

Change log

Fix✗ → ✓Sep 28, 2026, 10:45 PM UTC

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records

Noroxi analysis

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Data sources and verification

CNA: isc

CVE.org (CNA)Apr 25, 2025, 11:02 PM UTC
NVDJun 16, 2026, 10:00 PM UTC
FIRST EPSSSep 29, 2026, 12:00 AM UTC
OSV / GHSASep 30, 2026, 3:23 AM UTC

Each line is when that source was last processed for this record.

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