CVE-2018-5733 | 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.

Published: 2019-01-16 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2018-5733 is rated High Risk (69/100): CVSS High severity, with high exploitation likelihood (EPSS 20.24%, 97th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +5.76% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2018-5733

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 14.48% 20.24% +5.76%
2 2026-06-04 9.82% 14.48% +4.66%
3 2026-06-03 — 9.82% —

Full EPSS history (31 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2018-5733

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.9 3.0 MEDIUM
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.2 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2018-5733

OS Trackers for CVE-2018-5733

vendor priority summary link
alpine — CVE-2018-5733: 1 source package rows (dhcp); 8 state rows across 8 repos (3.10-main, 3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, edge-main); fixed 8, open 0. https://security.alpinelinux.org/vuln/CVE-2018-5733
debian not yet assigned CVE-2018-5733 not yet assigned priority: Debian including 1 source packages (isc-dhcp), 4 status rows across 4 suites (bookworm, bullseye, sid, trixie): resolved 4. https://security-tracker.debian.org/tracker/CVE-2018-5733
gentoo normal CVE-2018-5733: 1 GLSA(s) (201804-05), 1 atom(s) (net-misc/dhcp); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2018-5733
redhat medium — https://access.redhat.com/security/cve/CVE-2018-5733
suse medium CVE-2018-5733 severity moderate: SUSE including 301 source package names (amazon/suse-sles-15-sp1-chost-byos-v20210304-hvm-ssd-x86_64, amazon/suse-sles-15-sp1-chost-byos-v20220127-hvm-ssd-x86_64, …), 472 product×package rows across 93 product lines (Image SLES12-SP4-Azure-BYOS, Image SLES12-SP4-EC2-HVM-BYOS, … (93 product lines)): Fixed 243, Known Affected 181, Known Not Affected 48. https://www.suse.com/security/cve/CVE-2018-5733/
ubuntu medium CVE-2018-5733 medium priority: Ubuntu including 1 source packages (isc-dhcp), 5 status rows across 5 suites (artful, bionic, trusty, upstream, xenial): released 4, needs-triage 1. https://ubuntu.com/security/CVE-2018-5733

Affected software / configurations for CVE-2018-5733

Vendor Product Version Raw CPE
isc dhcp >= 4.2.0, <= 4.2.8 cpe:2.3:a:isc:dhcp:*:*:*:*:*:*:*:*
isc dhcp >= 4.3.0, <= 4.3.6 cpe:2.3:a:isc:dhcp:*:*:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:-:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r10:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r10_b1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r10_rc1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r11:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r11_b1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r11_rc1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r11_rc2:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r12:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r12_b1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r12_p1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r13:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r13_b1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r14:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r14_b1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r15:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r2:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r3:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r3_b1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r4:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r5:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r5_b1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r5_rc1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r5_rc2:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r6:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r7:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r8:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r8_b1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r8_rc1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r9:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r9_b1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:r9_rc1:*:*:*:*:*:*
isc dhcp 4.1-esv cpe:2.3:a:isc:dhcp:4.1-esv:rc1:*:*:*:*:*:*
isc dhcp 4.1.0 cpe:2.3:a:isc:dhcp:4.1.0:-:*:*:*:*:*:*
isc dhcp 4.4.0 cpe:2.3:a:isc:dhcp:4.4.0:*:*:*:*:*:*:*
redhat enterprise_linux_desktop 6.0 cpe:2.3:o:redhat:enterprise_linux_desktop:6.0:*:*:*:*:*:*:*
redhat enterprise_linux_desktop 7.0 cpe:2.3:o:redhat:enterprise_linux_desktop:7.0:*:*:*:*:*:*:*
redhat enterprise_linux_server 6.0 cpe:2.3:o:redhat:enterprise_linux_server:6.0:*:*:*:*:*:*:*
redhat enterprise_linux_server 7.0 cpe:2.3:o:redhat:enterprise_linux_server:7.0:*:*:*:*:*:*:*
redhat enterprise_linux_server_aus 7.4 cpe:2.3:o:redhat:enterprise_linux_server_aus:7.4:*:*:*:*:*:*:*
redhat enterprise_linux_server_aus 7.6 cpe:2.3:o:redhat:enterprise_linux_server_aus:7.6:*:*:*:*:*:*:*
redhat enterprise_linux_server_eus 7.4 cpe:2.3:o:redhat:enterprise_linux_server_eus:7.4:*:*:*:*:*:*:*
redhat enterprise_linux_server_eus 7.5 cpe:2.3:o:redhat:enterprise_linux_server_eus:7.5:*:*:*:*:*:*:*
redhat enterprise_linux_server_eus 7.6 cpe:2.3:o:redhat:enterprise_linux_server_eus:7.6:*:*:*:*:*:*:*
redhat enterprise_linux_workstation 6.0 cpe:2.3:o:redhat:enterprise_linux_workstation:6.0:*:*:*:*:*:*:*
redhat enterprise_linux_workstation 7.0 cpe:2.3:o:redhat:enterprise_linux_workstation:7.0:*:*:*:*:*:*:*
canonical ubuntu_linux 14.04 cpe:2.3:o:canonical:ubuntu_linux:14.04:*:*:*:lts:*:*:*
canonical ubuntu_linux 16.04 cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:*
canonical ubuntu_linux 17.10 cpe:2.3:o:canonical:ubuntu_linux:17.10:*:*:*:*:*:*:*
debian debian_linux 7.0 cpe:2.3:o:debian:debian_linux:7.0:*:*:*:*:*:*:*
debian debian_linux 8.0 cpe:2.3:o:debian:debian_linux:8.0:*:*:*:*:*:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

References for CVE-2018-5733

cvelogic Threat Intelligence