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Fencer Vulns
medium 5.9

CVE-2018-5733 json

A malicious client can overflow a reference counter in ISC dhcpd

published 2019-01-16 7 y ago modified 2026-06-17 4 mo ago also EUVD-2018-17502

cvss
5.9
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
20.2%
EPSS 20.2% chance of exploitation in 30 days, percentile 97%
public exploits
0
none known

Summary

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.

Patch / fix

  • isc-dhcp Debian 13, Debian 12 4.3.5-3.1

debian advisories DEBIAN-CVE-2018-5733

  • isc-dhcp Ubuntu 14.04 LTS 4.2.4-7ubuntu12.12
  • isc-dhcp Ubuntu 16.04 LTS 4.3.3-5ubuntu12.9
  • isc-dhcp Ubuntu 18.04 LTS 4.3.5-3ubuntu5

ubuntu advisories UBUNTU-CVE-2018-5733

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • dhcp RHEL 6 12:4.1.1-53.P1.el6_9.3
  • dhclient RHEL 6 12:4.1.1-53.P1.el6_9.3
  • dhcp-common RHEL 6 12:4.1.1-53.P1.el6_9.3
  • dhcp RHEL 7 12:4.2.5-58.el7_4.3
  • dhclient RHEL 7 12:4.2.5-58.el7_4.3
  • dhcp-libs RHEL 7 12:4.2.5-58.el7_4.3
  • dhcp-common RHEL 7 12:4.2.5-58.el7_4.3

red hat advisories RHSA-2018:0469RHSA-2018:0483

  • dhcp SLES 11 SP4, SLES 11 SP3-TERADATA, SLE Software Development Kit 11 SP4 +3 more 4.2.4.P2-0.28.8.1
  • dhcp SLES for SAP 12 SP3, SLES for SAP 12 SP2, SLES for Raspberry Pi 12 SP2 +6 more 4.3.3-10.14.1

suse advisories SUSE-SU-2018:0810-1SUSE-SU-2018:0810-2SUSE-SU-2018:0812-1

  • dhcp openSUSE Tumbleweed 4.4.2.P1-2.4

opensuse advisories openSUSE-SU-2024:10715-1

  • dhcp Alpine 3.20, Alpine 3.19, Alpine 3.18 +8 more 4.4.1-r0

alpine advisories ALPINE-CVE-2018-5733

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • dhcp Arch Linux 4.4.1-1

arch linux advisories AVG-646

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2018-5733 updated cvss 5.9

dhcp: Reference count overflow in dhcpd allows denial of service

  • Red Hat Enterprise Linux 5 dhcp
    affected: no fix planned “Will not fix”
  • Red Hat Enterprise Linux Client (v. 7) dhcp 4.2.5-58.el7_4.3, dhclient 4.2.5-58.el7_4.3, dhcp-libs 4.2.5-58.el7_4.3, dhcp-common 4.2.5-58.el7_4.3 Red Hat Enterprise Linux Client Optional (v. 7) dhcp 4.2.5-58.el7_4.3 Red Hat Enterprise Linux ComputeNode (v. 7) dhcp 4.2.5-58.el7_4.3, dhclient 4.2.5-58.el7_4.3, dhcp-libs 4.2.5-58.el7_4.3, dhcp-common 4.2.5-58.el7_4.3 Red Hat Enterprise Linux ComputeNode Optional (v. 7) dhcp 4.2.5-58.el7_4.3
    fixed: vendor fix RHSA-2018:0483
  • Red Hat Enterprise Linux Desktop (v. 6) dhcp 4.1.1-53.P1.el6_9.3, dhclient 4.1.1-53.P1.el6_9.3, dhcp-common 4.1.1-53.P1.el6_9.3 Red Hat Enterprise Linux Desktop Optional (v. 6) dhcp 4.1.1-53.P1.el6_9.3
    fixed: vendor fix RHSA-2018:0469
  • Red Hat Enterprise Linux for ARM and IBM Power LE (POWER9) Server (v. 7) dhcp 4.2.5-58.el7_4.3, dhclient 4.2.5-58.el7_4.3, dhcp-libs 4.2.5-58.el7_4.3, dhcp-common 4.2.5-58.el7_4.3 Red Hat Enterprise Linux for ARM and IBM Power LE (POWER9) Server Optional (v. 7) dhcp-devel 4.2.5-58.el7_4.3, dhcp-debuginfo 4.2.5-58.el7_4.3
    fixed: vendor fix RHSA-2018:0483
  • Red Hat Enterprise Linux HPC Node (v. 6) dhcp 4.1.1-53.P1.el6_9.3, dhclient 4.1.1-53.P1.el6_9.3, dhcp-common 4.1.1-53.P1.el6_9.3 Red Hat Enterprise Linux HPC Node Optional (v. 6) dhcp 4.1.1-53.P1.el6_9.3 Red Hat Enterprise Linux Server (v. 6) dhcp 4.1.1-53.P1.el6_9.3, dhclient 4.1.1-53.P1.el6_9.3, dhcp-common 4.1.1-53.P1.el6_9.3
    fixed: vendor fix RHSA-2018:0469
  • Red Hat Enterprise Linux Server (v. 7) dhcp 4.2.5-58.el7_4.3, dhclient 4.2.5-58.el7_4.3, dhcp-libs 4.2.5-58.el7_4.3, dhcp-common 4.2.5-58.el7_4.3
    fixed: vendor fix RHSA-2018:0483
  • Red Hat Enterprise Linux Server Optional (v. 6) dhcp-devel 4.1.1-53.P1.el6_9.3, dhcp-debuginfo 4.1.1-53.P1.el6_9.3
    fixed: vendor fix RHSA-2018:0469
  • Red Hat Enterprise Linux Server Optional (v. 7) dhcp-devel 4.2.5-58.el7_4.3, dhcp-debuginfo 4.2.5-58.el7_4.3
    fixed: vendor fix RHSA-2018:0483
show 5 more
  • Red Hat Enterprise Linux Workstation (v. 6) dhcp 4.1.1-53.P1.el6_9.3, dhclient 4.1.1-53.P1.el6_9.3, dhcp-common 4.1.1-53.P1.el6_9.3
    fixed: vendor fix RHSA-2018:0469
  • Red Hat Enterprise Linux Workstation (v. 7) dhcp 4.2.5-58.el7_4.3, dhclient 4.2.5-58.el7_4.3, dhcp-libs 4.2.5-58.el7_4.3, dhcp-common 4.2.5-58.el7_4.3
    fixed: vendor fix RHSA-2018:0483
  • Red Hat Enterprise Linux Workstation Optional (v. 6) dhcp-devel 4.1.1-53.P1.el6_9.3, dhcp-debuginfo 4.1.1-53.P1.el6_9.3
    fixed: vendor fix RHSA-2018:0469
  • Red Hat Enterprise Linux Workstation Optional (v. 7) dhcp-devel 4.2.5-58.el7_4.3, dhcp-debuginfo 4.2.5-58.el7_4.3
    fixed: vendor fix RHSA-2018:0483
  • Red Hat Enterprise Linux 8 dhcp, dhcp-libs, dhcp-relay, dhcp-client, dhcp-common, dhcp-server
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

20.24% chance of exploitation in the next 30 days, higher than 97% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.0 5.9 CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P

Affected products

  • ISC ISC DHCP

Classification

Weakness
  • CWE-190 Integer Overflow or Wraparound

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.